He thinks it too difficult.这句话的后半部分是宾语从句吧,为什么it后不加is呢,求详解

He thinks it too difficult.这句话的后半部分是宾语从句吧,为什么it后不加is呢,求详解
你上面的表述不正确,应该是：
He thinks it too difficult.to learn English well.
或者：He thinks it is too difficult.to learn English well.
句子成分分析1：
He 主语
thinks 谓语
it 形式宾语
too difficult.宾语补足语
to learn English well.不定式短语,做真正的宾语
句子成分分析2：
He 主语
thinks 谓语
it is too difficult.to learn English well.宾语从句 (宾语从句中的it作形式主语,真正的主语是不定式短语to learn English well)