电渣焊可一次焊接很厚的工件，并且（）坡口。
A.可以不开
B.必须开
C.需开“v”型
参考答案：A
教室的供电线路允许通过的最大电流为1.5 A，室内已安装了6只“220 V 30 W”的日光灯，能否再安装一台120 W的彩色电视机？
Research findings show we spend about two hours dreaming every might, no matter what
we _________ have done during the day. [ ]
A. should
B. would
C. may
D. must
