Absolutely. I didn't get B right during the contest.

My solution was to first check if all black cells formed only one connected component.

Then check all columns and files, and if on some of them not all black cells were contiguous, output "NO". In any other case, output "YES".

But that wasn't enough. One final consideration that didn't came to me during the contest was needed: For any two black cells i1,j1 and i2,j2, check if either i1,j2 or i2,j1 is black. If neither of them are black, output "NO". Then if none of the above applies, output "YES".