请阅读下面短文，根据所提供的信息，回答5个问题，要求所写答案语法正确，语义完整切题。

We all know doing exercise makes us healthy. But many of us don’t know which is better, to exercise in the day or at night. Dr. Yang, a famous sleep doctor, advises people to do outdoor exercise for at least 30 minutes a day in the daytime.

Dr. Yang has been doing research on sports and sleep for years. He finds out that those who exercise in natural light for half an hour every day have better sleep and more energy(能量). Dr. Yang himself gets up at 6:30 a.m. Then he usually takes a walk outside. Sometimes, he walks his two dogs in the park in the afternoon with his sunglasses left at home.

Many schools put Dr. Yang’s findings into practice. They made it a rule that students should do outdoor exercise once or twice a day. In some schools, students even formed outdoor running clubs. After some time, most students said they benefited(受益) a lot from outdoor exercise. Now they sleep better and concentrate(集中) more than their studies.

Some students are now thinking about inviting their teachers to join them in their daily runs.

（1）. According to Dr. Yang, when is it better to exercise, in the day or at night?

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（2）. What is Dr. Yang’s research about?

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（3）. What does Dr. Yang usually do after he gets up?

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（4）. How often do students do outdoor exercise in many schools?

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（5）. Who will some students invite to join in their daily runs?

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