For the energy levels in an atom which of the following statement(s) is/are correct?

Options

A. There are seven principle electron energy levels depend on quantum numbers n and l
B. The second principal energy level can have 4 subshell energy and contain a maximum of 6 electrons
C. The M energy level can have maximum of 32 electrons
D. The 4s sub energy level is at a lower energy than the 3d sub energy level