It is no doubt that...如果用这样的表示,it为形式主语,that从句是真正主语从句。名词no doubt作表语。名词做表语表示A=B这样的逻辑。但这里的逻辑却是that从句的内容是无疑的,而不是怀疑或不怀疑本身。因此,这里需要的是形容词作表语。如果一定要用it作形式主语,这个句子就得改为形容词做表语。如:It is doubtless that...。
There is no doubt that grades have improved and interest in education has revived.
无疑,成绩提高了,上学的兴趣也恢复了。
I have no doubt that we are polluting the environment beyond redemption.
我丝毫都不怀疑我们对环境的污染是不可挽回的。