下列作家，属于后期元杂剧作家的有（）A．白朴 B．宫天挺 C．郑光祖 D．乔吉

The story happened in________and the hero was in his________.[ ]

A．the 1840s；thirties  

B．the 1840s；thirty

C．1840s；thirties  

D．1840s；thirty

混凝土配制强度。与设计强度的关系是（）。

A.A

B.B

C.C

D.D

We should try every effort to prevent violence from happening at school, ______ more and more students would drop out of school ______ their personal safety could not be guaranteed.

A．though; if only

B．though; so long as

C．for; now that

D．for; if

DJ置接地位时，DJ的一端是与共阳极元件联接，DJ能否工作，完全取泱于DJ线圈两端（）是否足够大。

可使献血者产生不愉快经历的例子（）

A.没有足够的解释.说服工作

B.不卫生.不安全的环境

C.在献血前后对献血者和病人材料缺乏保密性

D.献血后不能提供足够的休息时间