What is the pig doing? The pig is ___________. [ ]
A. hugging
B. eating
C. sleeping
答案:C
Don't forget _____ the lights when you leave.[ ]
A. to turn off
B. turning off
C. turn off
D. turned off
超声探头最重要的部件是:
A:保护层
B:匹配层
C:压电振子
D:负极引线
E:探头导线