Do you play with your phone before bedtime? You may want to read a book instead. According to a US study, looking at screens(屏幕) at night can make us sleep poorly.

In the evening, our bodies make melatonin(褪黑素). Melatonin helps us feel sleepy and relaxed. It’s an important part of our sleep cycle(周期). The screens stop that cycle from working normally(正常地). Why? Phones, computers and TVs make blue light. Blue light stops our bodies from making melatonin. Even just a little bit of blue light can have an effect(影响). Eight minutes of blue light can keep your brain “awake” for another hour, according to the study. Even if you fall asleep, you may have lots of dreams. Your brain won’t have a good rest.

It’s even worse if you play an exciting game before bed. Games make our hearts beat faster, so we have a harder time falling asleep. Then, when we fall asleep, we don’t get enough “deep sleep”.

Imagine sitting in a boat in the ocean. The sky is blue, the sun is out, and the water is clear. Suddenly, you notice something moving in the water, so you stand up to get a closer look. 【小题1】 And it’s a fast swimmer. It jumps out of the water and then it’s gone. You’ve Just seen an orca（虎鲸）!

Orcas, also called killer whales, live in every ocean on Earth. 【小题2】 Firstly, orcas are not really whales. They’re in fact the largest member of the dolphin family. Secondly, they are usually harmless to humans. Orcas’ attitudes toward humans depend on human attitudes toward orcas.

Orcas are quite playful. They live in groups called “pods”, with between 5 and 30 orcas, for their whole lives. 【小题3】 The orcas’ friendly nature is very useful for finding food. Orcas hunt in their pods and then work together to kill.

There are about 40 orcas in aquariums（水族馆）all over the world. 【小题4】 The most famous orca, Keiko, who appeared in the film Free willy, was in an aquarium. Later scientists tried to help him go back to the wild. They were successful. Keiko became much healthier when he was moved from the aquarium to the sea. However, Keiko liked humans more than other orcas. 【小题5】

There are many natural mysteries and wonders in the world, here are some of them.

About 11,000 years ago, some ancient humans went for a muddy walk in Africa. They left more than 400 footprints, which became fossils. It’s the largest collection of ancient African footprints ever found. Scientists have studied all the footprints. And they have learned more about the people who left them. All of the footprints came from feet. Scientists found the footprints of 17 people who probably walked together. The footprints were all traveling in the same direction and at the same speed. From the size of the footprints, scientists think the group was mostly adult women. They may have been out gathering food together.

Can snakes be friends? Some scientists recently found the answer by closely watching 40 young garter snakes. These small, harmless snakes are common in North America. Scientists divided the snakes into 10 groups. Then they put each group into a small space together for eight days. They found that snakes do seem to have friends. Each snake liked to stay together with certain snakes more than others. Even when scientists moved them around, the snakes often went back to their same friends. Snakes are known for being unfriendly — but it’s not always true, scientists say.

All living things need water. But they get it in different ways. You drink water from a glass. Plants take it in with their roots (根). Koalas get water from eucalyptus (桉树) leaves they eat. But scientists have discovered that koalas have another way to get water: They lick (舔) trees. People noticed the surprising behavior while watching wild koalas in Australia. During rainstorms or right after, rainwater dropped down from tree trunks. Some koalas got the running water while they sat in the trees. One koala was so thirsty that it kept licking a wet tree trunk for more than 30 minutes without stopping.

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