英語句型的五大結構 拆解?

It is hard to please my teacher.
it = 虛主詞（形式上的主詞）
is =主要動詞
hard =主詞補語（形容詞）
to please my teacher =延遲的主詞（delayed subject）；「名詞性質的不定詞片語」
「不定詞片語」或「動名詞片語」常以虛主詞it取代，成為delayed subject，以免句子頭重腳輕。這樣句子較自然。

Variation of this pattern with introductory it, when the subject is an infinitive with a phrase:-
Rearranging the sentence:--
It is-----introductory it, with v
hard-----adv.
to be pleased for my teacher------subject ,an infinitive with a phrase.