阅读下面短文并回答问题，然后将答案写到答案纸相应的位置上(请注意题后的词数要求)。
[1]A new study has found evidence of aggressive behaVior in children who drink four or more servings of soft drinks every day．
[2]The mothers of 3，000 five-year-olds took part in the study．They were asked to keep a record of how many servings of soft drinks their children drank over a two-month period and keep records of how they behaved．The researchers found that 43 percent of the boys and girls drank at least one daily serving of soda．Four percent of the youngsters had four or more sodas to drink every day．
[3]Children who drank the most soda were more than two times likely to show signs of aggression．“For the children who consumed four or more  soft drinks per day，we see an association between aggressive behaviors, attention problems and withdrawn behaviors．”Shakira Suglia says．The aggressive behaviors included destroying possessions belonging to others，taking part in fights and physically attacking people.
[4]Shakira says the researchers identified the link after they considered the factors like the child’s age and sex．They also considered     ，such as whether the boys and girls were eating sweets or given fruit drinks on a normal day．In addition，the researchers examined parenting styles and other social conditions that might be taking place in the home.
[5]It is not quite clear why young children who drink a lot of soda have behavior pmblems．However，a substance oftell found in soft drinks is caffeine，which helps to make people feel energetic．Doctor Suglia suggests that caffeine could be causing the children to be more aggressive.
[6]The research is part of a larger study called the Fragile Families and Child Welibeing Study．It follows 5，000 poor mothers and their children in 20 American cities.
What is the main idea of the text?(no more than 10 words)
What does the underlined word“they’’in Paragraph 2 probably refer to?
List three aggressive behaviors according to the text．(no more than 10 words)
①
②
③
Fill in the blank in Paragraph 4 with proper words．(no more than 3 words)
Complete the following statement with one word from Paragraph 5．
People will often become      when they have some coffee，in which caffeine is the major chemical．