Research shows that afternoon naps — when timed correctly — do not negatively impact nighttime sleep. In multiple studies, people who took afternoon naps obtained as much or more sleep in a 24-hour period than those who didn’t nap. 

In most cases, the benefits of afternoon naps far outweigh (超过) any of the disadvantages. However, if you nap too late in the afternoon, or for too long, you may experience difficulties falling and staying asleep during the night. This can occur because daytime napping reduces your sleep drive, your body’s need for sleep. Because of this, most experts recommend avoiding naps after 3 p.m. to limit disruptions to your sleep schedule.

For people who maintain a traditional sleep-wake schedule, napping in the early afternoon (between 1 p.m. and 3 p.m.) is likely optimal. Many people naturally experience a period of decreased energy and alertness in the early afternoon, known as the “post-lunch dip” or “afternoon slump”. Napping during this time has been found to boost energy levels, increase alertness, improve mood, enhance memory and cognitive ability, and improve physical ability. In general, experts recommend limiting your nap to at least 8 hours before bedtime to avoid nighttime sleep problems. 

For most people, napping for 30 minutes or less will have the most beneficial effect.Shoter naps allow the body to get some light sleep without entering deep sleep. If you wake up during deep sleep, you may find yourself to be even groggier (昏昏沉沉的) than you were before the nap. In some cases, napping for 90 minutes can also provide substantial benefits. Napping for this length allows your body to cycle through the stages of sleep and avoids disrupting deep sleep.

If you find yourself frequently napping during the day, you may not be getting the recommended amount of sleep you need each night. If you still need naps despite getting enough sleep, talk to your doctor to assess your sleep quality and rule out any potential sleep disorders.

1.Why don’t experts recommend a nap late in the day?

A Because it increases your body’s need for sleep.

B Because it has negative effects on nighttime sleep.

C Because it’s difficult to fall asleep in the afternoon.

D Because it makes people experience a decline in energy.

解析：选B。B 细节理解题。根据第二段的“However, if you nap too late in the afternoon, or for too long, you may experience difficulties falling and staying asleep during the night.”可知如果你在下午睡得太晚，或者睡得太久，你可能会在晚上经历入睡和保持睡眠困难，即它对夜间睡眠有负面影响。故选B。

2.What does the underlined word “optimal” probably mean?

A Best.

B Relaxing.

C Fastest.

D Accurate. 

解析：选A。A 词义猜测题。结合划线词所在句后面的“Napping during this time has been found to boost energy levels, increase alertness, improve mood, enhance memory and cognitive ability, and improve physical ability.”可知，在这段时间小睡可以提高能量水平，提高警觉性，改善情绪，增强记忆力和认知能力，并提高身体能力，即在下午一点到三点之间小睡是“最佳的”。故选A。

3.What’s does the fourth paragraph focus on?

A The quality of naps.

B The benefits of naps.

C The duration of naps.

D The drawbacks of naps.

解析：选C。C 段落大意题。根据第四段第一句“For most people, napping for 30 minutes or less will have the most beneficial effect.”对大多数人来说，小睡30分钟或更少会有最有益的效果；结合后文的关键词句“Shorter naps”“napping for 90 minutes”以及“Napping for this length”等，可知本段主要描述小睡的持续时长。故选C。

4.What’s needed when you still experience sleep loss after enough sleep?

A Napping for more than 30 minutes.

B Going to bed an hour earlier.

C Asking for professional help.

D Trying to get up later than usual.

解析：选C。C推理判断题。根据最后一段最后一句“If you still need naps despite getting enough sleep, talk to your doctor to assess your sleep quality and rule out any potential sleep disorders.”可知，如果你在睡眠充足的情况下仍然需要小睡，即仍然感到睡眠不足，那你需要和你的医生谈谈，寻求专业帮助。故选C。