[单选题]
The total mechanicalzrp8ogr gbk3shmr f;p 34 8c (8).:rd q-iturt energy oses9k 1 //dflif a system
A. is equally divided between kinetic energy and potential energy.
B. is either all kinetic energy or all potential energy, at any one instant.
C. can never be negative.
D. is constant, only if conservative forces act.
