【题目】The waste water has been made clean before it goes into the river ________ the new rule was made.
A.when
B.ever since
C.after
D.before

【答案】B
【解析】句意：自从新规则被制定以来，在废水进入河流之前，就已经被处理干净了。when当……时；ever since自从；after在……之后；before在……之前；主句中使用现在完成时，说明应该使用ever since引导这个时间状语从句。故B正确。