it's not something you need to do.在河北版八年纪第59课hobby

it's not something you need to do.在河北版八年纪第59课hobby
it's not something you need to do.
在河北版八年纪第59课hobby

it's not something you need to do.在河北版八年纪第59课hobby
something这件事你不必做,但已经做了or特指双方都知道的某类事.
其他还有表示说话人肯定,希望发生/出现的事物.

什么在哪用啊????

在哪用?