计算（﹣a﹣b）2等于[ ]
A．a2+b2
B．a2﹣b2
C．a2+2ab+b2
D．a2﹣2ab+b2
答案：C
The postcards often remind me _____ my old friends. [ ]
A. at
B. for
C. of
D. with
发电厂及变电所的中央信号按用途分为哪几类？
