题目

 Tom often               in the morning, so his mother bought him an alarm clock to wake him up on time.        A. exercised     B. forgot          C. walked            D. overslept 答案：D如右图所示，将一小气球套在装有氮气的试管口．把试管放在盛有热水的水槽中，小气球变大．当气球变大时，关于试管中的氮气分子，下列说法正确的是（　　）A．氮气分子变大B．氮气分子间间隔变大C．氮气分子数增多D．氮气分子变成氧气分子