What is the difference between ...

我諗你嘅"It + is + adjective + pronoun + to inf "　　應該係
"It + is + adjective +ｏｆ＋ pronoun + to inf "

"It + is + adjective +ｏｆ＋ pronoun + to inf "係要黎形容人
例如：
it is nice of her to help the elderly.

"It + is + adj+ that " 係要黎形容事件／事物
例如：
it is nonsensical(無意義的) that the government decides to improve the air qualilty without action.