【单选题】The case was crushed. It looks _________ the case was not strong enough to stand voyage.
【判断题】整流电路的功率因数为电网侧有功功率与视在功率之比。()
【多选题】邮件收发系统中用户可以使用邮件系统提供的功能,其中发件人可以发邮件,邮件发送后收件人可以收邮件,那么这一系统的参与者和用例是哪些?
【简答题】若char ch='b',那么遇到下列语句会输出______。 switch(ch) {case'a':printf("it is a\n"); case'b':printf("it is b\n"); case'c':printf("it is c\n");break; case'd':printf("it is din");)