American high school students who slept less than seven hours each night during the pandemic(流行病) were more likely to have difficulty in school. That finding comes from a study from the U.S. Centers for Disease Control and Prevention, or CDC.

For the study, the CDC questioned 7,705 students about their sleep schedules and success in school. More than two-thirds of students said they experienced more difficulty in their schoolwork during the pandemic than before the pandemic. About 75 percent of students did not sleep enough during the pandemic, the study found.

Students who reported poor mental(心理上的) health during the pandemic were also more likely to get less sleep. 37 percent of students said they struggled with their mental health during the pandemic. But about 50 percent of students who slept five hours or less each night said they had poor mental health.

Teenagers experience many physical changes when they go through puberty(青春期). _________ As children get older, there is a change in their body’s natural clock. Before puberty, children may feel sleepy around 8 or 9 at night. But when they become teenagers, the body’s clock changes to make them tired much later—around 10 or 11 at night. Because of this, many teenagers may experience the difficulty in sleeping.

Some schools around the U.S. are pushing back start times for high schools so students can get more sleep. Usually, high schools start the earliest compared to middle and primary schools. The organization Start School Later supports the idea. It says at least 13,000 schools in the United States have changed start times.

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1.What can we know from Paragraphs 2 and 3?

A 7,075 students were questioned in the study.

B 2300 students had difficulty studying during the pandemic.

C The length of sleeping time can influence mental health.

D Half of students did not sleep enough in 2020.

解析：选C。C推理判断题。根据第三段最后一句“But about 50 percent of students who slept five hours or less each night said they had poor mental health.”可知，但约50%每晚睡眠时间不超过5小时的学生表示，他们的心理健康状况不佳，由此可知睡眠时间长短和心理健康状况可能有一定联系。故选C。

2.Which can be put back into the blank?

A Puberty can also cause changes in sleep patterns.

B A good sleep schedule can improve test performance.

C Teenagers should sleep 8 to 10 hours a night.

D The results are from younger students in the country.

解析：选A。A推理判断题。根据空白部分后面的“As children get older, there is a change in their body’s natural clock.”可知，青少年在青春期会经历许多身体变化，随着孩子们年龄的增长，他们身体的自然时钟发生了变化。在青春期之前，孩子们可能会在晚上8点或9点左右感到困倦。但当他们成为青少年时，身体的时钟会发生变化，使他们在晚上10点或11点左右才感到疲劳。因此“青春期也会导致睡眠模式的改变”最衔接上下文。故选A。

3.What is the last paragraph mainly about?

A Why students sleeping well do better on tests.

B When is the best time for students to go to bed.

C How parents like the Start School Later.

D What schools did to improve students’ sleep.

解析：选D。D段落大意题。该段主要讲了美国各地的一些学校正在推迟高中生的上学时间，以便学生能够获得更多的睡眠。故选D。

4.What do the underlined words “pushing back” mean?

A Looking for.

B Putting off.

C Getting on.

D Waking up.

解析：选B。B词义猜测题。根据后面的“get more sleep”和“Start School Later”可知，为了让学生能够获得更多的睡眠，美国各地的一些学校正在推迟高中生的上学时间。故选B。

5.Where can the text be found?

A In a history book.

B In a novel.

C In a health magazine.

D In a notebook.

解析：选C。C推理判断题。本文主要讲了一项研究发现：睡眠时间越少，成绩可能越差。属于健康类文章，故我们可以在健康杂志读到。故选C。