it"s +adj+that是什么意思it"s +adj+that+从句时如何用的?

it"s +adj+that是什么意思
it"s +adj+that+从句时如何用的?

it"s +adj+that----,是主语从句.
it 是形式主语.如:
it's nice that she helped me with my homework.
另外that不可省略.