A system of non-interacting spin-1/2 charged particles are placed in an external magnetic field. at low temperature t, the leading behavior of the excess energy

A system of non-interacting spin-1/2 charged particles are placed in an external magnetic field. At low temperature T, the leading behavior of the excess energy above the ground state energy, depends on T as: (c is a constant) a. cT b. CT3 C. e d. c (is independent of T)