In windless weather, raindrops fall vertically in the air, and finally fall at a constant speed because of air resistance. This constant speed usually

Test and analysis: let the raindrop mass be m and the closing speed be v, then there is

It can be seen that the greater the mass of raindrops, the greater the closing speed. Therefore, A is right and C is wrong; Raindrops fall vertically in the air under the action of gravity and air resistance. Because air resistance is directly proportional to the speed of raindrops, at the beginning, air resistance is less than gravity, and raindrops accelerate downward. With the increase of speed, the air resistance increases and the resultant force decreases. According to Newton's second law, the acceleration decreases. When air resistance and gravity are balanced, raindrops move in a straight line at a uniform speed, and the maximum speed reaches the terminal speed, then raindrops move with decreasing acceleration and increasing speed before the terminal. So b is correct.