u=5sin(20t+30°)V与i=7sin(30t+10°)A的相位差为30°。
参考答案:错
假设雅典某年的全国人口约25万人,自由民约为16万8千人,其中男性成年公民约4万5千人,外邦人约3万人,奴隶约1万人,其中有权参加公民大会的人数是约[ ]
A、16万8千
B、4万5千
C、7万5千
D、12万8千
He felt ____ he alone were responsiblefor what had happened. [ ]
A. as if
B. in case
C. while
D. though