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这句before后面从句时态的用法是怎么回事?

来源:学生作业帮 编辑:作业帮 分类:英语作业 时间:2024/05/10 23:27:20
这句before后面从句时态的用法是怎么回事?
you must first establish the primary cause of waste generation before attempting to find solutions.
efore 后面的是you attempt to find solutions的省略形式.又如:Knock at the door before entering.=Knock at the door before you enter .