队列研究的特点为（）
A.属描述性研究
B.所需时间短
C.不设对照
D.采用前瞻性的方法
E.是"从果到因"的研究
参考答案：D
—My car _____ twice this month.
—I'm sorry to hear that.[ ]
A. has been broken in
B. was broken in
C. has been broken into
D. was broken into
此次疾病流行的传播途径最有可能是
A．接触疫水
B．苍蝇
C．注射途径
D．水源或食物污染
E．密切接触
