电视信号占用的频率范围很宽,一套电视信号的频带宽度为()。
A.3MHz
B.6MHz
C.8MHz
D.10MHz
参考答案:C
根据对话意思和所给首字母,写出完整正确的单词
Millie: You look w__小题1:______. What’s happening?
Amy: There’s too much homework. I must c__小题2:____ it before I go to
bed . And I always have no time for my h__小题3:____.
Millie: I think you should a____小题4:____ a balance between them. Maybe you
can ask Mr Wu to give you some s___小题5:_____
下列哪一条是错误的()
A.队列研究中暴露组发病率/对照组发病率等于相对危险度
B.在病例对照研究中,病例组发病率/对照组发病率等于相对危险度
C.在队列研究中,被观察人数×被观察时间之积是人年数
D.病例对照研究中的相对危险度是对角乘积比
E.特异危险性是暴露组死亡率(发病率)-非暴露组死亡率(发病率)之差,常用于卫生宣教时