概率抽样的理想类型是（）
A.分层抽样
B.等距抽样
C.简单随机抽样
D.整群抽样
参考答案：D
—If you have any trouble, be sure to call me.
—_______.
A．I am glad to hear that
B．I will. thank you very much.
C．I have no trouble
D．I will think it over
腹部最易损伤的空腔脏器是（）
A.结肠
B.胃
C.小肠
D.直肠
E.十二指肠
