题目

题型：不详难度：来源：

The waste water, when _______，should be clean enough to meet standards.

A．releasing

B．being released

C．released

D．to be released

答案

C

解析

试题分析：句意：废弃的水在排放时，应该被净化到符合标准。When引导时间状语从句，完整的句子应该为“When the waste water is released, it should be clean enough to meet standards.”当从句主语和主句的主语一致，而且从句谓语动词为be动词时，从句中的主语和谓语动词可以省略，故原句可以省略成“When released, the waste water should be clean enough to meet standards.”故选C。