When a raindrop falls, it increases in size and so its mass at time t is a function of m(t). The rate of growth of the mass is km(t) for some positive constant k. When we apply Newton's Law of Motion,
(a) The acceleration of the raindrop decreases with time.
(b) The acceleration of the raindrop increases with time.
(c) The acceleration of the raindrop remains constant.
(d) The acceleration of the raindrop is zero.