在流行病学研究当中必须设立对照的有
A．横断面研究
B．病例对照研究
C．队列研究
D．临床试验
E．社区实验
参考答案：B,C,D,E
下列关于点对点短信息业务正确的描述是（）
A.短信按条计费，发送方收费，接收方免费
B.短信业务必须定制开通才可使用
C.点对点短信业务转发信息不收费
D.主叫计费按照发送号码的归属分为长途短信及市内短信两种
Which statement about Airbus is false().
A. It currently leads the way in China with a 64% market share.
B. It has invested heavily in China.
C. It takes a 36% market share in China.
D. It manufactures parts and transfers technical know-how in China.
