i think （）important to tell him about it。答案是it ，为什么不是it‘s呢一般做形式主语都是ti✀s开头

两个答案都可以，都对，句子结构不同，分析如下：
　　I think it important to tell hime about it.是简单句，第一个it是形式宾语，为真正宾语。
　　I think it is important to tell hime about it.是主从复合句，it is important to tell hime about it.是宾语从句，从句中，第一个it是形式主语，to tell hime about it.作真正主语。

两种都是对的。
I think it important to tell him about it. think+it+important是think+宾语+宾语补足语的用法，it代指句中后面的to tell him about it.
I think it's important to tell him about it.这句中it's important to tell him about it是从句，即think+从句的用法

it是形式宾语，important是宾语的补语，to tell him about it是真正的宾语。用it is 也可以的，这样it is important to tell him about it就是宾语从句，it成为形式主语。

it 形式宾语 你认为的用it is 的话是一个i think （that） it is important to tell him about it 还是用形式主语 应该说语法上面也是正确的 只是有点烦而已。 一般当两个结构可以表示一个意思的时候，用简单的那个。

对，你说的没错，括号的前身就是it's， 我高一的时候老师解释过，具体忘记了，不过就是，填it 和it's 是一个样的，填it's就是连个句子普通拼接起来嘛，而it就是另外一个语法，忘记名称了。我知道答了等于没答