Energy of a spring-mass oscillator increases if

T=2πmK  and  K=mω2 for a spring-mass system. Total mechanical energy = 12KA2.For (A): Since, energy depends on K, A, changing mass does not change energy.For (B): Same explanation as for (A).For (C): Maximum kinetic energy (which is at mean position) = Total mechanical  energy =  12KA2It is independent of mass, only depends on K of spring, and amplitude of motion.