跌水井常用（）和溢流堰式两种类型。

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问题填空题

跌水井常用（）和溢流堰式两种类型。

答案

参考答案：竖管式

选择题

16. He made another wonderful discovery, __________ of great importance to science.

A．I think which is

B．which I think it is

C．which I think it

D．which I think is

问答题简答题

古代社会与现代社会的特点？