[单选题]
A mass is attached to a vertical spring and bobs up a:br 3 g(zt6:v6 qqxhhund down betwh;fk lnuq ,*4ween points A and B. Where is the mass located ;ufn4 qkh,w*lwhen its kinetic energy is a minimum?
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
