电焊机的结构要（），各接触点和连接件应牢靠
A.整齐
B.简便
C.合理
D.便于维修
参考答案：C, D
Before the child went to bed,the fater asked him to ________ all the toys he had taken out.
A．put off
B．put up
C．put away
D．put out
幼年时生长素分泌不足可引起（）
A.侏儒症
B.呆小症
C.肢端肥大症
D.地方性甲状腺肿
E.向心性肥胖
