下列哪一种指标常用来说明疾病对人的生命危协程度（）。
A、发病率
B、死亡率
C、患病率
D、罹患率
E、病死率
参考答案：E
— Watch!
— I ____ but ____ I ____ anything unusual. [ ]
A. watched; have watched
B. have watched; am not seeing
C. was watching; wasn't seeing
D. am watching; don't see
两个软件都属于系统软件的是
A．DOS和Excel
B．DOS和UNIX
C．UNIX和WPS
D．Word和Linux
