A、Caffeine. B、Sex. C、Sweets. D、Characters. A短文最后提到Suglia博士认为软饮巾的咖啡因可能会导致五岁的孩子变得更加有侵略性。该处是唯一处提到原因的，故选A。

A new study found that 43 percent of boy and girl participants drank at least one daily serving of soda. Four percent of the youngsters had four or more sodas to drink every day.
     [22]The study’s author, Shakira Suglia says her team found that children who drank the most soda were more than two times as likely as those who drank no soda to show signs of aggression. For the children who consumed four or more soft drinks per day, they see an association between aggressive behaviors, attention problems and withdrawn behaviors.
     [23]The aggressive behaviors included destroying possessions belonging to others, taking part in fights and physically attacking people.
    Shakira Suglia says the researchers identified the link after they considered socio-demographic factors like the child’s age and sex. They also considered other possible influences, such as whether’ the boys and girls were eating sweets or given fruit drinks on a normal day.[24]In addition, the researchers examined parenting styles and other social conditions that might be taking place in the home.
    Doctor Suglia says it is not clear why young children who drink a lot of soda have behavior problems. A substance often found in soft drinks is caffeine, which helps to make people feel energized.[25]She suggests that caffeine could be causing the five year olds to be more aggressive.
22. What did the researchers find from the study?
23. What did the aggressive behaviors include according to the passage?
24. What factors did the researchers consider before they identified the link?
25. What is supposed to be the cause of the aggressive behaviors according to Doctor Suglia?