before 后面跟动词ing 是什么结构啊

Question

before goinh to bed,turn the lights off,,这个结构在句中充当什么成分 有人说介宾结构那这个结构做射成分

Answer 1

before是介词，后接动名词，构成介宾结构。追问

那介宾做什么成分

追答

作为介宾结构，通常作状语用，也可做定语、表语、补语等，这里是时间状语。

Answer 2

before 和 after 后经常可以加动词现在分词，省略主语,主语要前后一致
比如：
Before you go to bed, turn the lights off.
Before going to bed, turn the lights off.
再比如：After I planted the trees, I felt tired. 可改成：
After planting the trees, I felt tired。
Before he did his nomework，he drank a glass of water．
Before doing homework, he drank a glass of water.本回答被网友采纳

Answer 3

before可作介词或连词，连词+句子，介词+动词ing/名词/代词。如：
Before he came here,he bought some presents.=Before coming here, he bought some presents.
类似的还有after.