题目内容：

Have you ever experienced the feeling of falling as you start to fall asleep? Sometimes you may come to realize this feeling. If so, don’t worry. Many people have felt the same thing.

In fact, these muscle twitches (肌肉抽搐) in the arms, legs or other parts of the body are called hypnic jerks (入睡抽动) or sleep starts. And they are very common. Up to 70 percent of people experience them sometimes, Huffington Post reported. But what causes it?

There are some theories(理论). Some scientists believe that the feeling of falling comes from the body relaxing itself, especially if the person is anxious or unable to get comfortable. As you’re about to sleep, your muscles become relaxed. But your brain stays awake. It misunderstands the relaxing of your muscles as a sign that you’re falling.

Then the brain jerks the body awake as if it’s trying to protect you.

    Other scientists believe that different phases of sleep might cause the hypnic jerks. When we sleep, we experience two phases: non-rapid eye movement (NREM) and rapid eye movement (REM). During REM, our heart rate (心率), breathing and nervous system can act irregularly (不规律地). If the body experiences flashes (一瞬间) of REM while entering sleep, these irregularities could cause twitches.

If you don’t want to experience hypnic jerks, scientists have some suggestions. When you become deeply relaxed, you can learn how to reconnect slowly by moving your fingers and toes a little bit. Then start to move your head and open your eyes, while being aware of yourself as you get out of the relaxed state.

But experts agree that hypnic jerks, though sometimes scary, are harmless. If it wakes you up, simply roll over and go back to sleep. But keep in mind: a caffeinated (含咖啡因的) drink, exciting evening activities or stress may make hypnic jerks happen more often.

1.The third paragraph mainly tells us_____________.

A. there are all kinds of theories about hypnic jerks

B. different phases of sleep might cause hypnic jerks

C. People sometimes get anxious or uncomfortable

D. the feeling of falling comes from the body relaxing itself

2.How many theories on what causes hypnic jerks are mentioned?

A. Two    B. Four    C. Three    D. Five

3.Which of the following can make hypnic jerks happen more often?

(1)Drinking caffeinated drink            (2)Singing songs for a long time before sleep

(3)Too much stress                    (4) reading a book quietly

A. (1)(2)(3)    B. (1)(2)(4)    C. (2)(3)(4)    D. (1)(3) (4)

4.What is the best title?

A. How to Experience Hypnic Jerks    B. What causes Hypnic Jerks

C. Feelings of Falling While Going to Sleep    D. Sleeping Is Good for Our Health