Q1. What is the passage mainly about?

1. AWhy students feel sleepy in afternoon classes
2. BHow to make classes more interesting
3. CWhat to eat for lunch
4. DHow teachers can stay awake

午後の授業で眠くなる3つの理由を説明しているので A。

Q2. According to the passage, when does the body clock make us a little sleepy?

1. AEarly in the morning only
2. BIn the early afternoon
3. CLate at night only
4. DRight after waking up

our body clock makes us a little sleepy in the early afternoon とあるので B。

Q3. In this passage, "hidden" means ...

1. Avery loud
2. Beasy to see
3. Cnot seen or noticed
4. Dvery short

hidden は hide（隠す）の過去分詞で「隠れた、見えない」なので C。

Q1. What did the 1998 survey find?

1. AStudents who ate more lunch were sleepier.
2. BStudents who exercised more got lower grades.
3. CStudents who slept more felt sleepier during the day.
4. DStudents who slept less and went to bed later felt sleepier and tended to get lower grades.

those who slept less and went to bed later felt sleepier during the day and tended to get lower grades とあるので D。

Q2. What is the "post-lunch dip"?

1. AA natural drop in alertness in the early afternoon
2. BA type of lunch dish
3. CA short exercise after lunch
4. DA rise in energy after eating

Alertness naturally drops a little in the early afternoon, and this "post-lunch dip" とあるので A。

Q3. According to the passage, why does sleepiness appear when sitting quietly?

1. ABecause quiet rooms are too warm
2. BBecause there is little to stimulate the brain, so existing sleepiness shows
3. CBecause students eat too much
4. DBecause teachers speak too fast

there is little to stimulate your brain, so sleepiness that was already there comes to the surface とあるので B。

Q1. What happened in the 2017 Singaporean experiment?

1. AWeekend sleep fully restored attention.
2. BAttention improved without naps.
3. CAttention steadily declined without naps and was not fully restored by weekend sleep.
4. DStudents slept ten hours on weeknights.

those who did not nap showed steadily falling attention, which two nights of weekend recovery sleep did not fully restore とあるので C。

Q2. What does the author mean by "Boredom does not create sleepiness so much as reveal it"?

1. ABoredom shows sleepiness that was already there.
2. BBoredom is the main cause of sleep debt.
3. CBoring classes make people sleep at night.
4. DBoredom has nothing to do with sleepiness.

退屈は眠気を生むのではなく、もともとある眠気を表に出すという意味。sitting still and listening lets existing sleepiness rise to the surface とも説明されているので A。

Q3. Which limitation of the 1998 survey is mentioned?

1. AIt studied only adults.
2. BIt used brain scans.
3. CIt lasted only one day.
4. DIt was cross-sectional and self-reported, so it cannot show cause and effect.

That survey was cross-sectional and self-reported, so it cannot show that short sleep caused the poor grades とあるので D。