hard homework question

sounds good man

 

The riddle may also be asking why manholes are round and not square thus needing round rather than square covers. In that case, the answer would be that you can not drop a round cover into the round hole but a square cover can be dropped into a square hole. In fact it would be easier to drop a square cover into the hole than to cover the hole. Thus the answer would be that a round cover would never need to be fished out of the bottom of a manhole.