Minimizing $2$ DFA's can be done in $O(n log n)$ time using Hopcroft's algorithm.
So there exists a polynomial time algorithm to do so but
For a given NFA of n state, number of states in equivalent DFA is atmost $2^n$.
Worst case complexity is $O(2^n)$
Hence B is not a P problem
Similarly comparing 2 regex will require to first convert both regex to NFA and then to DFA which will also not take polynomial time
So $A$ is correct answer