原式=a+2-a+2(a+2)(a-2)•(a+2)(a-2)
=4.
Mary feels ________ because she lost her watch this morning. [ ]
A. sad
B. ill
C. happy
D. frightened
在发送筒的主管三通之后和接收筒大小头前的直管上()左右,应安装收发球指示器。
A.1m
B.2m
C.3m
D.4m