If someone asked me why manhole covers were round, my answer would be that it is because manholes are round.
For question 6, the spinning disc, it says "unknown" for the answer. Does that mean the author doesn't know the answer, or is the correct answer that the solution to this problem is not known?
For question 6, the spinning disc, it says "unknown" for the answer. Does that mean the author doesn't know the answer, or is the correct answer that the solution to this problem is not known?