it's no good...thre is no need...为什么?那些词用it's...哪些用there is ...

it's no good...thre is no need...
为什么?那些词用it's...哪些用there is ...

it's 是"主系表"结构,是说一个东西怎么怎么样,例如,好/坏,大小,颜色...等等
比如: it's not bad.
there is 表示"有"
比如: there is a cup on the desk.
桌子上有个杯子

四个字 ：地道英语