跌落式开关的常见故障有（）、（）、（）。
参考答案：熔丝管烧损，熔丝管误跌落，熔丝误断
Now Bob is _____________ than he was. [ ]
A. more carefully
B. much careful
C. more careful
D. much carefully
乳牙列阶段是（）
A.2.5~6岁
B.6个月~2.5岁
C.3~5岁
D.13~15岁
