赤磷着火点比黄磷高得多,易燃____。
A.且易自燃
B.且遇湿自燃
C.但不易自燃
参考答案:C
The news reporters hurried to the airport, only the film stars had left. [ ]
A. to tell
B.told
C. telling
D. to be told
超声换能器(探头)的作用是()
A.发射超声波
B.接收超声波
C.发射和接收超声波
D.放大超声波
E.滤过超声波