I think it is__(use）to learn Chinese well

I think it's for you to learn Chinese well I think it’s very空(use) to learn a foreign language well I think it's(use)to study English well I find it hard （to learn） Chinese well 为什么是to lea I think it necessary to learn english well.同义句 Do you think it's ___(use) to learn English well? I think——（this,that,it）is very useful to learn english well. I think that it is important to learn English well .(改为简单句） I think ____ to learn English well. LeArn English well,I need to use it.哪里错了 I think it easy to learn English well.这里it后怎么没is? I think it difficult to learn English well句中为什么用it?