应当是It's important for sb. to do sth.因为It's+形容词+for/of sb. to do sth. 是一个句式用of 时形容词修饰人（即sb.）如：It's good of you to help me .用 for 时修饰事情（即sth.）如：It's impossible for you to do it.
It's important for sb to do sth
