普查妇女乳腺癌时测量疾病的频率指标应选用（）。
A.期间患病率
B.时点患病率
C.罹患率
D.发病专率
E.发病率
参考答案：B
It be difficult to get a train ticket during traditional Chinese Spring Festival this year because there are many ticket windows.
A．mustn't
B．ought to
C．needn't
D．can't
计算机通信网中传输的是 。
A．数字信号 B．模拟信号 C．数字或模拟信号 D．数字脉冲信号
