题目内容：

阅读下面短文，并根据所读内容在文章后表格中的空格里填入一个最恰当的单词。

注意:请将答案写在答题卡上相应题号的横线上。每个空格里只填一个单词。

Many of us have had this experience: we lie down in a bed other than our own, perhaps at a friend’s house or in a hotel room, and find it difficult to fall asleep.

Why does it happen?

A new study shows one reason is what the scientists call “first night effect”. They believe that one side of the brain acts as a “night watch” to warn us about possible dangers. It prevents us from getting to sleep on the first night in a new environment.

For the study, 35 young volunteers were asked to sleep in a sleep lab for several days as researchers watched their brain activities.

According to the researchers, on their first night, the left brain was more active than the right brain and people had a hard time sleeping. However, the left brain activity decreased(降低) as days went by, falling even to the point of complete calm. In this process, the volunteers got better and better sleep experience.

The findings show that the different rhythms(节奏) of the sides of the brain affect our sleep. When the two sides work differently, the balance between them is broken. So the brain can’t relax and is sensitive(敏感的) to anything strange around.

“At some level, the brain is continuing to work, even though you don’t realize it,” US professor Jerome Siegel told Smithsonian Magazine. “If something unusual happens, you can be alert(警惕的)”.

More surprisingly, this is like the way some animals sleep. Whales, dolphins, and many birds can sleep with half of their brain while the other half stays awake, with one eye staying open.

The researchers think that it is the result of evolution(进化) and works to protect us in possibly dangerous environments.

If you have ever had first night effect, researchers advise you to bring your own pillow or sleep in a room similar to your bedroom next time you sleep away from home.

First night effect
People’s possible experience	Many people have 1. getting to sleep on the first night in a new environment.
The findings of the study	♦First night effect forces us to stay awake as one side of the brain is alert to possible dangers. ♦As days go by, people’s sleep experience 2. as the left-brain activity falls.
The explanations to the findings	♦On the first night in a new environment, people’s left brain is more active than the right brain and that 3. the balance between them. ♦Our brains continue to work without being realized at night so that we can be sensitive to anything unusual. ♦Some other animals sleep in the similar way, which is thought to be 4. by evolution.
5. from researchers	Bring your own pillow or sleep in a bedroom that looks like yours.