it is hard to think of a world without you

you think it is a good habit to study hard it is hard to think of a world without you It is hard for him to think for himselfxie It is hard to Do you think it ever approprite to give up that you think is too hard? I think it hard to fall asleep in night.请问it后为什么不加is. I think it hard to fall asleep in night.为什么it后面没有is I think it important to study hard和l think it is important to study hard哪个句子是对的?为什么? I think it important to study hard和l think it is important to study hard哪个句子是对的?为什么? Do you think the problem is hard If you think hard ,you 'll find it easy to work out 为什么选hard 和easy 还有例句 It is hard to wait It is hard to please It is hard to select! 关于think is,英语语法例句：I think it is hard to say.这是什么结构?为什么两个动词可以连用? 请问如何将'' I think it is hard to learn English well '改为否定句. do you think it is a good habit to study hard是写一篇英语作文 Is that true that it's hard to be a person?I don't think so! IT is hard to think of a world without metals什么句型