1.be useful to_______ 2.be helpful to______3.be important to______4.be necessary to______

Question

填doing或do

Answer 1

be useful to do sth

it is helpful to do sth. 做……是有好处的
It is helpful for sb. to do sth. 某人做……是对他有好处的
这两个都是it 做形式主语
helpful 是表示“有好处”，而不是“有助的”
it is helpful in doing sth.
sth. is helpful to sth./ doing sth. 前面的sth.一般是具体的某个事物

be important to do sth ,be important for sb to do sth

be necessary to do sth

Answer 2

It's useful \helpful \ important \necessary to do sth

在这个句型中通常是to do

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不对吧，我记得be helpful to doing sth

追答

在上面句型中是to do
在下面短语中可以出现doing，不过doing是动名词，不能理解为现在分词，并且这种用法比较少，如果有名词意义的词就不用doing动名词
sth. is helpful to sb. ……对某人有助

....is helpful to sth. 对……有助

Answer 3

write

think

sleep

study

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