The chair looked rather hard,but in fact it is very comfortable to sit on.

题目

The chair looked rather hard,but in fact it is very comfortable to sit on.
各路英语才子们,小妹不知道句子中为什们会有个on,麻烦各位想想,给个回答,

答案

因为sit 是不及物动词,必须有一个介词on在后,才能连接宾语chair