Tornadoes are nature's most violent storms, which can cause deaths and destroy a neighborhood in seconds. A tornado appears as a funnel-shaped (漏斗状) cloud from a thunderstorm to the ground with whirling (飞快移动) winds that can reach 300 miles per hour. Damage paths can be over one mile wide and 50 miles long. Every state is at some risk from this disaster.

    Some tornadoes can be seen clearly, while rain or nearby low-hanging clouds obscure others. At many times, tornadoes develop so rapidly that little, if any, advance warning is possible.

    Before a tornado hits, the air may become very still. A cloud of debris (散片) can mark the location of a tornado even if a funnel can not be seen. Tornadoes generally occur near the edge of a thunderstorm, when the strong wind may die down. It is not uncommon to see clear, sunlit skies behind a tornado.

The following are facts about tornadoes:

    The average forward speed of a tornado is 30 MPH, but may also vary from still to 70 MPH. Debris is picked up or a cloud forms in the funnel.

    The average tornado moves from southwest to northeast, but tornadoes have been known to move in any direction. Tornadoes are most often reported east of the Rocky Mountains during spring and summer months.

    Tornadoes can happen together with tropical storms and hurricanes as they move onto land. Waterspouts are tornadoes that form over water.

    The tornado season in the southern states of America is March through May; in the northern states, it is late spring through early summer. Tornadoes are most likely to occur between 3 p.m. and 9 p.m., but can occur at any time.

    Every day, Americans throw away 500 million plastic straws, enough to circle the Earth twice. They are almost never recycled, and simply contribute to the great problem of plastic pollution; eight million tons of plastic is dumped into the oceans every year.

    Plastic straws are now the target of a growing movement to reduce their use. Possibly the first of such campaigns, Be Straw Free was started in 2011 by Milo Cress, who was only nine years old at the lime.

"I noticed that whenever I ordered a drink at a restaurant, it would usually come with a straw in it, and I don' I usually need a straw," he said. "This seemed like a huge waste. Straws are made of oil, a precious and finite resource. Is making single - use plastic straws, which will be used for a matter of minutes before being tossed away, really what we want to do with this resource?"

    Cress started asking restaurants in Burlington, Vermont, where he lived at the time, to stop providing straws automatically to customer and make them optional instead. Many agreed and his request made ripples (涟漪) nationwide. The restaurants that make the switch report a reduction in the number of straws they use between 50 and 80%.

    The anti - straw sentiment has crossed borders into the UK, where straws have been included in a government plan to ban ail plastic waste by 2042.

Last year large pub chain Wetherspoons announced that it would replace plastic straws with paper alternatives across 900 outlets. After the announcement, many smaller chains and pubs across the country followed suit. According to Wetherspoons CEO John Hutson, the move will save 70 million plastic straws a year and the reaction from patrons has been "very positive".

Offering alternatives or making plastic straws optional, rather than banning them completely, is a common trait among these campaigns. "There are many other viable alternatives to single - use plastic drinking straws that are less harmful to the environment, wildlife and humans," said Jackie Nunez, founder of The Last Plastic Straw.

    It is important to protect yourself from harmful rays. But if you think a high-factor sunscreen keeps you safe from harmful rays, you may be wrong. Research in this week's Nature shows that while factor 50 reduces the number of melanomas（黑瘤）and delays their occurrence, it can't prevent them. Melanomas are the most aggressive skin cancers. You have a higher risk if you have red or blond hair, fair skin, blue or green eyes, or sunburn easily, or if a close relative has had one. Melanomas are more common if you have periodic intense exposure to the sun. Other skin cancers are increasingly likely with long-term exposure.

    There is continuing debate as to how effective sunscreen is in reducing melanomas – the evidence is weaker than it is for preventing other types of skin cancer. A 2011 Australian study of 1,621 people found that people randomly selected to apply sunscreen daily had half the rate of melanomas of people who used cream as needed. A second study, comparing 1,167 people with melanomas to 1.101 who didn't have the cancer, found that using sunscreen routinely, alongside other protection such as hats, long sleeves or staying in the shade, did give some protection. This study said other forms of sun protection – no sunscreen – seemed most beneficial. The study relied on people remembering what they had done over each decade of their lives, so it's not entirely reliable. But it seems reasonable to think sunscreen gives people a false sense of security in the sun.

    Many people also don't use sunscreen properly applying insufficient amounts, failing to reapply after a couple of hours and staying in the sun too long. It is sunburn that is most worrying – recent research shows five episodes of sunburn in the teenage years increases the risk of all skin cancers.

    The good news is that a combination of sunscreen and covering up can reduce melanoma rates, as shown by Australian figures from their slip-slop-slap campaign. So if there is a heat wave this summer, it would be best for us, too, to slip on a shirt, use sunscreen and slap on a hat.

    You're out to dinner. The food is delicious and the service is fine. You decide to leave a big fat tip. Why? The answer may not be as simple as you think.

    Tipping, psychologists have found, is not just about service. Instead, studies have shown that tipping can be affected by psychological reactions to a series of different factors from the waiter's choice of words, to how they carry themselves while taking orders, to the bill's total. Even how much waiters remind customers of themselves can determine how much change they pocket by the end of the night.

    “Studies before have shown that mimicry(模仿) brings into positive feelings for the mimicker,” wrote Rick van Baaren, a social psychology professor. “These studies show that people who are being mimicked become more generous toward the person who mimics them.”

    So Rick van Baaren divided 59 waiters into two groups. He requested that half serve with a phrase such as. “ Coming up !” Those in the other hall were instructed to repeat the orders and preferences back to the customers. Rick van Baaren then compared their take-home pay. 'The results were clear—it pays to mimic your customer. The copycat(模仿者) waiters earned almost double the amount of tips to the other group.

    Leonard Green and Joel Myerson, psychologists at Washington University in St. Louis, found the generosity of a tipper maybe limited by his bill. After research on the 1,000 tips left for waiters, cabdrivers, hair stylists, they found tip percentages in these three areas dropped as customers' bills went up. In fact, tip percentages appear to plateau(稳定期) when bills topped $100 and a bill for $200 made the worker gain no bigger percentage tip than a bill for $100.

    “That's also a point of tipping,” Green says. “You have to give a little extra to the cabdriver for being there to pick you up and something to the waiter for being there to serve you. If they weren't there, you'd never get any service. So part of the idea of a tip is for just being there.”

    Judy Wright and her husband decided to move closer to their son, Chris, who lived in Georgia. About a month after the move, Judy fell ill, suffering from her ongoing battle against Parkinson's disease.

    Her condition worsened rapidly and she required medical care at home. The family hired a nursing aid who canceled at the last minute. Instead, a woman named TunDe Hector showed up in her place.

    One day, TunDe shared a story with Judy and her family. She remembered a particularly difficult day in 2014, when a stranger had helped her with a kind gesture. She had run out of gas, and with only$5 in her pocket, was walking to a gas station, gas can in hand. A man saw her walking and turned his car around. He paid for her gas and gave her all the cash left in his wallet. Upon hearing the story, Judy's son, Chris, took off his hat and said, "That was me!” He was the stranger that had helped TunDe on that difficult day.

    During the care of Judy, the Wright family learned about TunDe's family and her own dream. The nursing aid, TunDe hoped that one day she could become an OB-GYN nurse.Her tuition was past due(逾期) and she had a family to care for, but she was determined to achieve that goal for herself and her family.

    Judy died on July 9,2017. Instead of flowers, her family asked mourners(悼念者) to donate to TunDe's education , to assist her in paying for her nursing school. In less than a week, they raised more than $8,000 and presented her with the surprise check.

    The famous director of a big and expensive movie planned to film a beautiful sunset over the ocean, so that the audiences could see his hero and heroine in front of it at the end of the film as they said goodbye to each other forever. He sent his camera crew out one evening to film the sunset for him.

    The next morning he said to the men, "Have you provided me with that sunset?"

    "No, sir," the men answered.

    The director was angry. "Why not?" he asked.

    "Well, sir," one of the men answered, "we're on the east coast here, and the sun sets in the west. We can get you a sunrise over the sea, if necessary, but not a sunset."

    "But I want a sunset!" the director shouted. "Go to the airport, take the next flight to the west coast, and get one."

    But then a young secretary had an idea. "Why don't you photograph a sunrise," she suggested, "and then play it backwards? Then it'll look like a sunset."

    "That's a very good idea!" the director said. Then he turned to the camera crew and said, "Tomorrow morning I want you to get me a beautiful sunrise over the sea."

    The camera crew went out early the next morning and filmed a bright sunrise over the beach in the middle of a beautiful bay. Then at nine o'clock they took it to the director. "Here it is, sir," they said, and gave it to him. He was very pleased.

    They all went into the studio. "All right," the director explained, "now our hero and heroine are going to say goodbye. Run the film backwards so that we can see the 'sunset' behind them."

    The "sunset" began, but after a quarter of a minute, the director suddenly put his face in his hands and shouted to the camera crew to stop.

    The birds in the film were flying backwards, and the waves on the sea were going away from the beach.