He says that it's important to learn English well改为被动语态

He says that it's important to learn English well改为被动语态

That the English is important to be learned well is said by him
He says that English is important to be learned well.
不知道你要哪句.

He says that it's important for English to be learned well

That it's important to learn English well is said by him.

It is said by him that English is important to be learned well.
主语从句作主语时，前面可以用形式主语it，希望我能帮助你解疑释惑。