When was the last time someone unexpectedly did something nice for you? Not someone you knew, but a total stranger? It's happened to me a few times, but two instances really stand out.

    A few years ago, I was dining in a restaurant with a friend who kept talking about himself, completely not aware of the fact that I was sitting there in misery. It wasn't my friend's talks that made me suffer. I was recovering from a broken heart, and just sitting down to dinner reminded me of my last relationship. I could have burst into tears right there at the table.

    When we picked up the check, the waitress said, ―Your meal was already paid for.  My friend and I didn't have a clue how it happened. Then I remembered a man coming in out of the corner of my eye. He was dressed in mostly white, sat down at the bar, had a beer, and stayed for maybe ten minutes. The waitress said, ―Yes, the gentleman in white paid for you.  It felt like an angel was saying ―I see you, honey. It's going to be okay.

    Just last year, I was running a half-marathon. With just 1 mile to go, I was out of gas. Runners call it ―hitting the wall . I thought I couldn't move another inch. Out of nowhere, a stranger came up to me and said, ―What's your name, sweetie? Jennifer? Okay, Jennifer, let's go! Come on! It's just around the corner! You can do it!  And he ran with me until I picked up my pace. I found him at the finish line to thank him for the encouragement only to learn he wasn't even supposed to be in the race that day.

    I still shake my head when I think of these momentary angels that came to me at my point of need.

    Do you have any experiences like these?

    John is a mechanic, but he lost his job a few months ago. He has good heart, but always feared applying for a new job.

    One day, he gathered up all his strength and decided to attend a job interview. His appointment was at 10 am and it was already 8:30. While waiting for a bus to the office where he was supposed to be interviewed, he saw an elderly man wildly kicking the tyre(轮胎) of his car. Obviously there was something wrong with the car. John immediately went up to lend him a hand. When John finished working on the car, the old man asked him how much he should pay for the service. John said there was no need to pay him; he just helped someone in need, and he had to rush for an interview. Then the old man said, "Well, I could take you to the office for your interview. It's the least I could do. Please. I insist." John agreed.

    Upon arrival, John found a long line of applications waiting to be interviewed. John still had some grease(油脂) on him after the car repair, but he did not have much time to wash it off or have a change of shirt. One by one, the applicants left the interviewer's office with disappointed look on their faces. Finally his name was called. The interviewer was sitting on a large chair facing the office window. Rocking the chair back and forth, he asked, "Do you really need to be interviewed?" John's heart sank. "With the way I look now, how could I possibly pass this interview?" he thought to himself.

    Then the interviewer turned the chair and to John's surprise, it was the old man he helped earlier in the morning. It turned out he was the General Manager of the company.

    "Sorry I had to keep you waiting, but I was pretty sure I made the right decision to have you as part of our workforce before you even stepped into the office. I just know you'd be a trustworthy worker. Congratulations!" John sat down and they shared a cup of well-deserved coffee as he landed himself a new job.

    Mr. Lee was in bed and was trying to go to sleep when he heard the bell ring. He turned on the light and looked at his clock. It was twelve o'clock. "Who can it be at this time of night?" He thought. He decided to go and find out. So he got of bed, put on his dressing gown (浴袍) and went to the door. When he opened the door, there was nobody there. "That is very strange." Then he went back to his bedroom, took off his dressing gown, got back into bed ,turned off the light and tried to go to sleep.

    A few minutes later he heard the bell again. Mr. Lee jumped out of bed very quickly and rushed to the door. He opened it, but again he found no one there. He closed the door and tried not to feel angry. Then he saw a piece of paper on the floor. He picked it up. There were some words on it : "It is now after midnight(午夜), so it is April Fool's Day (愚人节). April fool to you!"

    "Oh, it was the English boy next door!" Mr. Lee exclaimed (惊叫) and almost smiled. He went back to bed and feel asleep at once. The bell did not ring again.

    A new officer with the Huntington Park Police patrols (巡逻) local parks 24 hours a day seven days a week. He doesn't need rest, coffee breaks, a salary or medical insurance, and that is because it is a Robocop.

    The main function of the Robocop is to scan and film the surroundings. Besides cameras with night vision that report 360 degrees, it also has a distress button which is located here, so if somebody is to need assistance or they want to contact the communication center, they can do it by way of that distress button. There are people that are monitoring on the other end.

    This newest police employee is self-charging. It's easy to program it and make changes to the software if necessary. Its maintenance (维护) costs are roughly 75 thousand dollars a year. It travels the entire park. It is a programmed path, but the police are able to change the path and adapt it.

    The Robocop can record the license plates (车牌) of passing cars and check them against an online database of stolen cars. It can also help locate a lost iPhone because it is able to determine a smartphone's MAC address. The police can see from the robot if something wrong happens and then come and figure it out.

    The Robocop can't replace its human handlers. The whole goal is to give police more time to do things machines can't do. The police have been having some concerns about safety of the parks and want an extra set of eyes that will help patrol a 24/7.Robocop's creators believe this model known as K5 is best used for providing security at public places like hospitals, parking lots, parks and airports. So far, it seems to be working out just fine.

This winter, the U. S. state of California received unusually large amounts of rain and snow. Now, people worry that some areas will flood as the snow in the Sierra Nevada Mountains melts (融化).

Ron Caetano lives about half-way between the cities of Los Angeles and San Francisco. He is preparing to leave in case his community, called the Island District, floods.

More than 100 years ago, the Island District area was under a large lake named Tulare Lake. At one time, Tulare Lake was the largest freshwater lake west of the Mississippi River. But reservoirs (水库) and watering systems for agriculture caused it to disappear. However, in very rainy years, farmland can still get covered with water.

Experts say reservoirs near the area will likely receive three times more water than they can hold this year. That means officials must increase the amount of water they release (释放) from the reservoirs. If too much water is released, the area might flood.

The Island District has organized a community network to help prepare for floods. People are placing sandbags close to elderly neighbors' houses to block possible flooding. And they are looking at reports from water officials, county officials, and from each other.

California has had very dry weather in recent years. Both cities and farm communities acclaimed this year's winter rains. If the weather gets warmer slowly, the snow will not melt quickly and there may be little or no flooding. But if the weather gets hot quickly, that will bring trouble from too much melting snow.

Officials announced plans to close parts of Yosemite National Park because of threats of flooding. The park is about 270 kilometers east of San Francisco in the Sierra Nevada Mountains.

Nicholas Pinter is with the University of California, Davis Center for Watershed Sciences. He said the lake's size has always changed because of California's weather. He described the surrounding area this way. "It has been an engineering problem all along," he said. "This is a bathtub (浴缸) with no way out."

"What beautiful music!" I shout loudly as my 9-year-old son practices playing the violin. He's used to this praise; I give rewards like that most days. But every once in a while, I skip it, and when I do, I can see the disappointment on his face when he's finished.

Am I a bad mom? Conventional wisdom says that consistency is key to parenting since it enables your child to predict how you'll react, leading to good behavior. And it's true that children need some level of predictability in their lives, particularly when it comes to discipline.

But research suggests that inconsistent gifts and praise can have a greater effect on motivation. While we all like to live in a predictable world, we often respond more strongly to unpredictable rewards.

In one experiment, my colleagues and I told participants they'd be paid if they could drink about one-and-a-half quarts of water in two minutes or less. In one condition, we offered people a $2 fixed reward. In another, there was an uncertain reward of either $2 or $1. The certain reward was a better deal, yet many more people successfully met the challenge when assigned an uncertain reward. Resolving the uncertainty—whether they would win $1 or $2—was significantly more motivating than winning $2 for sure.

Here is one of the reasons why uncertainty is motivating. What scientists call "intermittent (间歇性) reinforcement" —rewarding behavior on some but not all occasions—makes it morearduous to know when rewards will show up. If you very often, but don't always, praise your child for completing their chores, they'll keep up the good behavior in the hope of receiving praise the next time.

So don't assume that if kids are always praised for finishing their homework, they'll be more likely to do it. Do praise young people for a job well done, just not every time. And pick rewards out of a hat when they complete chores—the surprise prize might keep everyone motivated to get things done.