Assume that chemically equivalent protons show the same signal while chemically non-equivalent protons show different signals. For the following molecules MM to PP, how many sets of signals would be observed in their $^1$H NMR spectra? Label all protons in each molecule with numbers, so that the protons that give the same NMR signal are labeled with the same number, and protons that give different signals are labeled with different numbers.
MM
NN
OO
PP
Br
N
Cl