接地导线采用的是()导线。
A.铜芯
B.铝芯
C.任意材料
D.复合线缆
参考答案:A
The headmaster _______ be in the office because the light is off. [ ]
A. can't
B. might
C. could
D. must
优级淡色啤酒的浊度应在()EBC单位以下,瓶装酒泡沫应在()秒以上。