[单选题]
A mass is attached to a vertical spring and bobs up s ble(dwo/g/n0 j6of;and dowhs n8ga3-xwu wiq56t- n between points A and B. Where is the mass located wh6snqx g-3w i5h-u8wtaen 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
