[单选题]
A mass is attached to a vertical spring and bobs ez gsme,+p 21yup and di 4 nj53k/ddt*lf .vvlown between points A and B.*.idlftvk d 45jv3ln/ Where is the mass located when its kinetic energy is a maximum?
A. at either A or B
B. midway between A and B
C. one-fourth of the way between A and B
D. none of the above