what to do属于:疑问词+不定式的结构,通常在句子中做主语、宾语或者表语。
Where to go has not been decided. 做主语
The problem is how to get the money. 做表语
I think what to eat is not important. 做宾语
by doing 是介词+动名词的结构,表示 通过做....,一般放在句首或者句末作为状语。
We will decide which one to choose by carring them out in practice.
我们通过在实践中使用来决定选择哪个。
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