Which shows the sub-levels in order of increasing energy in the fourth energy level of an atom?

A.     ${\text{f}} < {\text{d}} < {\text{p}} < {\text{s}}$

B.     ${\text{p}} < {\text{d}} < {\text{f}} < {\text{s}}$

C.     ${\text{d}} < {\text{f}} < {\text{p}} < {\text{s}}$

D.     ${\text{s}} < {\text{p}} < {\text{d}} < {\text{f}}$

D