阅读下面短文，并根据短文后的要求答题（请注意问题后的字数要求）。
［1］If you are worried about things and are under a lot of stress at work or school，then you are prob-ably not sleeping well. Worry can keep you awake，tossing and turning in bed until the early hours of the morning when you eventually fall asleep. When you wake up，you don't feel refreshed，but tired and worn out and unable to face a new day.
［2］ Dr. Henry Winkle，in a recent newspaper article entitled Stress and Sleep，indicates that       .Dr. Winkle says，“The more we worry，the less we sleep，the more we are unable to deal with stress. If  we can find a way to get a good night's sleep，”he adds，“we can often find the energy to deal with what's worrying us.”
［3］So，what is a good night's sleep? Research shows that the amount of sleep which people need in order to keep healthy varies a lot. Seven hours is about the average amount，though strangely enough，sleeping longer often gives you a headache instead of making you feel more refreshed.
［4］Dr. Winkle believes that preparing for sleeping is important. People who work late should try to give themselves a short break and do something restful before going to bed. This could be watching TV or listening to music. Doing some exercise earlier in the day should help you to feel physically as well as mentally tired. A bedtime drink can also help，but coffee or tea should be avoided as they contain caffeine and will keep you awake.
［5］ “When you put the light out，” Dr. Winkle says，“concentrate on relaxing your muscles，working slowly up from your feet，and you 'll be asleep before you know it.”
What is the main idea of the text? (no more than 5 words)
                                                             
Complete the following statement with words from Paragraph 2. ( no more than 3 words)
People shouldn't go to sleep immediately but should          after working late in the night.
Point out the disadvantage of drinking coffee and tea before going to bed. (no more than 6 words)
                                                             
Fill in the blank in Paragraph 2 with proper words. (no more than 10 words)
                                                             
What does the word “it” (Line2，Paragraph5) probably refer to? (no more than 3 words)