1. An object of mass m is observed to move in a straight line with velocity given by v = bt² − ct, where b and c are positive constants. The expression for the force on the object as a function of time is
(A) mbt² − mct
(B) 2mbt² − 2mct
(C) 2mbt − mc
(D) mbt − mc
(E) mbt² − 0.5mct

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