单项选择题
A 550 N physics student stands on a bathroom scale in an 850 kg (including the student) elevator that is supported by a cable. As the elevator statts moving, the scale reads 450 N. The acceleration of the elevator is .
A、17.82m/s^2, upward
B、17.82m/s^2, downward
C、1.78m/s^2, upward
D、1.78m/s^2, downward
A.
B.82m/s^2,
C.82m/s^2,
D.78m/s^2,
E.78m/s^2,