A) Given an nfa with n states, there could be 2^n states in its equivalent dfa in the worst case (each of its states being a unique combination of n states of the nfa). Hint: Try to remember the conversion of an nfa into dfa.
B) Take for instance, an nfa for L = 0* which requires only one state but could have many more with epsilon transitions. It could be minimised into a dfa with only two states. So, n can be greater than m.
C) A dfa can have more than one final state.
D) See B.
So, answer is A.