形容词加to do与名词加to do有何区别?

it 是形式主语,it 代替to climb the tall tree爬高树这件事.在英语里,动词短语作主语时,爱用it来代替动词短语,把动词短语放在面,避免头重脚轻.原来是这样表达的：To climb the tall tree is dangerous. 爬高树是危险的.dangerous危险的,作表语,表示爬高树这件事的状况用形容词来描述危险的.danger 危险 抽象名词,不可数名词,不能用在这里,但是要注意,抽象名词具体化时,又成可数名词,如： To climb the tall tree is a danger.爬高树是一件危险的事.或者It is a danger to climb the tall tree .又如：It is a pleasure to see you.见到你是一件快乐的事.It is pleasant to see you 见到你真快乐.