瓦斯继电器内气体的颜色一般说明变压器发生何种故障？
参考答案：黄色不易燃气体表明木质故障，灰白色有臭味可燃气体表明纸及纸板故障，灰黑色易燃气体表明油故障。
— You look very pale. You ____ very tired.
— I didn't sleep at all last night. [ ]
A. must be
B. must have been
C. can be
D. can have been
日内瓦学派（或称认知学派）的创立者是（）
A.弗洛伊德
B.皮亚杰
C.瓦龙
D.霍尔
