关于平流沉淀池的表述正确的是______。
A．造价较低
B．占地面积大
C．一般用于大、中型净水厂
D．排泥较方便
参考答案：A,B,C
—Where is Peter? —He _____ to Shanghai.
A．went
B．had gone
C．has been
D．has gone
----Does Liu Hua serve in the army?
----No,but he ___in the army for three years.
A．served
B．has served
C．is serving
D．would serve
