They consider it harmful to do sth 这句语法有错吗?it后为什么没is,consider后为什么没that

同学.
当不定式作find,think,feel,consider等动词的宾语,且有名词或形容词作宾语补足语时,必须使用it作其形式宾语,相当于其后所接的宾语从句.例如
Some students find it difficult to study English = Some students find (that) it is difficult to study English.一些学生发现英语很难学
Bill Gates feels it his duty to help the poor = Bill Gates feels (that) it is his duty to help the poor.比尔·盖茨觉得济贫是他的义务.
I think / consider it wrong to do like that = I think / consider (that) it is wrong to do like that.我认为那样做是错误的
注意
在“find / think / consider / feel 等 + it + n./ adj.+ to do sth.”句型中,当宾语补足语是“no use或no good”时,“to do sth.”应改用“doing sth.”.例如
I think it no use fighting each other.我认为彼此开战没什么用
I feel it no good only remembering the grammar rules in language learning.