Dogs are our friends. With them, we won’t be alone. However, dogs can do us even more good than that. They can help children improve their reading skills.

A team of Canadian scientists did an experiment (实验) with 22 boys and 17 girls in grades one through three. They first tested their reading abilities. Then they asked them to read books that were somewhat difficult for them. Each child read aloud. After they finished the first page, scientists asked the children if they would like to read more or just stop there. They found that children spent more time reading and showed more interest when a dog was in the room. “Dogs can help children feel more confident (自信的),” scientists said.

Dogs are good listeners. They won’t mind if children make mistakes. They won’t stop children, either. They only stay quiet by the side of the children.

In recent years, therapy (治疗) dogs have taken part in reading activities in schools and libraries. This study helps us understand how dogs help children learn to read better.

Dragonflies fly around in the morning or evening of summer, but how much do you know about us?

Do trees stop growing? The answer is both yes and no. The trunks (树干) of trees keep getting wider,【小题1】. But, in fact, trees do stop growing in height. You can notice the similar height of the trees when you see a stand of trees of the same species (物种).

Just like people, the slowing in the growth of trees is related to their age. Trees grow more slowly as they age. At a certain age, they necessarily stop gaining height.【小题2】. But by the time the tree reaches 90 years of age, its growth has slowed to about half a meter--about a foot and a half- a year. By the time the tree is 150 years old, height growth has almost stopped, even though the tree may live another 100 years.

Some scientists suggest that tree cells ( 细胞 ) are like animal cells: that is,【小题3】. If a tree's cells stop dividing, then it stops getting taller. Another idea is that a tree's height is limited by the way it carries water from its roots to its leaves. Inside a tree, water moves upward, pulled towards the leaves. Some scientists put forward an idea that once a tree reaches old age and is tall enough, the downward pull of gravity (重力) makes it more and more difficult for the tree to pull the water all the way to its upper branches ( 树枝 ) and leaves.

So do trees stop growing? They do, and they don't. At some point, their height is more or less fixed at the same height as other trees of that kind.【小题4】.