If you are riding a bike in foreign countries, you need to know what these traffic signs mean.

1		This sign means “walk”, you can cross the street along with other people.
2		This sign is the “don't walk” sign. It means you should stop to wait for a while until the sign of “walk” is showing.
3		This sign means that there is a bike lane. If you see such a sign, you must use the bike lane.
4		Car drivers and bike riders must come to a complete stop at “STOP” signs.
5		This sign means you are coming to a zebra crossing. You must slow down to allow people in the zebra crossing to cross the street.
6		This sign means parts of the road are rough. Be careful! Rough roads make you fall off your bike.

    Many people have dogs at home as pets. If a dog is happy, then he may want to meet you or play with you. If he doesn't feel happy, then he would rather stay alone. But dogs can't talk. How can you tell how your dog is feeling? By his body language.

    If your dog's head and back are lowered, his ears are down and his eyes are narrowed, and his tail is between his legs, then he is fearful. You may touch him gently to comfort him. If your dog's ears are up, his eyes are bright, and he wags his tail rapidly (快速地), he is very happy. He may also hold his mouth open more or even pant (气喘) mildly. Then you can go and play with him freely. If he closes his mouth and looks serious as you get closer, then he has changed his mind. It is better to leave him alone until he comes to you. Remember, we are talking about dogs that you know. Be sure a parent is around to allow you to get close to the dog. Get away from strange dogs even if they seem friendly.

    The most important clue (线索) is the mouth. If the dog's mouth is closed, then he is most likely to be not relaxed or happy, and he does not want you to touch or play with him right now.

    Is it a bird? Is it a plane? No, it's your online shopping! Imagine a world where your shopping was dropped off on your doorstep by a delivery (投递) drone (无人机). Well, many companies are working to make this idea a reality. Among them, Amazon and UPS are just some of the front runners in the race to have the first ever business drone delivery service.

Pros:

    ①Fast. Delivery drones can cut down the time of delivery to just 30 minutes.

    ②Environmentally friendly. Companies like UPS have started that the use of drones would cut down on waste gas (气体).

    ③Cheap. Though exact prices for drone delivery aren't known, companies such as Amazon suggest deliveries could be as cheap as $1.

    ④Emergencies. Drones can fly straight to areas they're needed without using any roads.

From Dispatch (分派) to Doorstep:

    Usually products available for drone delivery will be stored somewhere nearby. Customers will choose these products through shopping apps or websites. The suggested weight to be carried is no more than 2.3 kilograms. Once the products are put into the drone, it will take off from the dispatch center. It will fly below 120m and avoid any "No Fly Zones" like airports for safety reasons. Before landing, a pad will be placed in the customer's garden for the drone's landing. After the drone puts down its product, it will rise to return to the dispatch center. So a drone delivery could one day be just a touch of an app with your finger.

Cons:

    ①Weather like strong winds, lightning storms and heavy rainfall may influence deliveries.

    ②Dispatch centers will have to be built within certain distance.

    ③Drones might be unable to land safely in high-rise buildings.

    ④Something will have to be done to make sure about the safety of the products and of people walking below.

    The future of flying transportation

    Though the delivery drone service is alive with new technology, we are a long way from seeing them through the air. There are still many difficulties such as flight law making. It's said that by 2021 we might see the beginning of drone delivery systems in action.

    What is the most stressful (有压力的) thing in school? It is probably exams. Exams can put us under a lot of stress. But some students do better under stress, while others do not. So, why do some students behave better under stress?

    It all comes down to dopamine (多巴胺). Dopamine is a chemical in our body that sends signals in the brain. It has many important roles: influencing memory, attention and how we learn.

    Our brains work best when there is a balance (平衡) of dopamine—not too much or too little. Our brains control dopamine in two ways. It either takes out dopamine quickly, or bit by bit. Exam success can be connected to how fast dopamine goes back to a balance, according to new research from the University of Missouri, reported Yahoo.

    What happens when we take an exam? If you become stressed, your brain will start to overload on dopamine. It is like a cup overflowing with water. The quicker you are able to go back to a balance of dopamine, the quicker you can focus, helping you do better on a test.

    Scientists found that, during a test, people who slowly got back to a balance of dopamine scored 8 percent lower. That's the difference between a good mark and a bad mark.

    But don't fear, there is good news for every student. The study also found that the more practice you get, the less stressed you will be. So, it turns out that     .

    Nowadays, computers and Internets are playing an important part in our life. Some people even say they can't live without them. We usually need to set passwords (密码) when we use computers and Internet. But not all the passwords are safe. In order to keep our accounts (账户)and personal information safe, we must learn how to make safe passwords.

    How can you make your computer and Internet passwords safe? Experts have some advice for you. You'd better remember the advice and they are useful for you. Here are the suggestions.

    Firstly, make your password out of capital(大写) letters. If your password is made of capital letters, it will be difficult for others to get into your account. It only takes a hacker(黑客) 10 minutes to work out a six- letter password made of small letters. But the same password in capital letters takes 10 hours to work out.

    Secondly, add numbers or symbols to your passwords. It may be much safer. Sometimes such password is not easy to remember, but it is really safe.

    Thirdly, never use personal information for passwords and use different passwords for different accounts. Experts say that a user should change his or her passwords every 90 days. In this way, hacker won't guess your passwords.