单项选择题

A.(N1+N2)[(3/2)kT+(5/2)kT]
B.(1/2)(N1+N2)[(3/2)kT+(5/2)kT]
C.N1(3/2)kT++N2(5/2)kT
D.N1(5/2)kT++N2(3/2)kT