形式主语句型结构是指一个句子中，主语部分由it或这类词语来代替实际主语，而真正的主语则放在后面的动词或介词短语中。这种句型结构常用于强调某个动作或情况的重要性，或者在需要特别强调某个句子成分时使用。下面是一些常用it作形式主语的句型结构：
1. It is important to study hard.（努力学习很重要。）
2. It takes me ten minutes to get to work.（我需要十分钟上班。）
3. It seems that she is not coming.（看起来她不会来。）
1. It is + adj. + to-infinitive: It is essential to exercise regularly.
2. It + linking verb (e.g. seems, appears, looks) + adj. + that-clause: It seems that he is not feeling well.
3. It + verb + obj. + to-infinitive: It takes a lot of effort to learn a new language.
4. It + verb + obj. + that-clause: It surprised me that she didn't know the answer.
形式主语的4种句型：
1. It is + adj. + to-infinitive：重要的是做运动。
2. It + 连系动词 (如seems, appears, looks) + adj. + that-从句：他看起来不太舒服。
3. It + 动词 + 宾语 + 不定式：学习一门新语言需要很大的努力。
4. It + 动词 + 宾语 + that-从句：她不知道答案让我感到惊讶。