[单选题]
An object of mass m is hanging by a stry8 /id:qslj/cjc 5 e*ping from the ceiling xn)t( 3f6q+ (bmdcsq ig,k/ib of an elevator. The elevator is moving up at constant speed. Whati)i q/ bq3n,(mx s(fd+ktg6cb is the tension in the string?
A. less than mg
B. exactly mg
C. greater than mg
D. cannot be determined without knowing the speed
