as a raindrop falls from a cloud to the surface of Earth<

1)its speed increases due to gravity
2)its speed increases due to air resistance
3)it moves at a constant speed

4)it moves at a constant velocity

I think # 3

number 3. the direction of the fall changes due to wind, so constant velocity is out.

The correct answer is #1, its speed increases due to gravity.

Explanation:
As a raindrop falls from a cloud to the surface of the Earth, it experiences the force of gravity acting upon it. Gravity is the force that pulls objects towards the center of the Earth. Since the raindrop is being pulled downwards, its speed increases as it falls due to gravity.

Air resistance, which is the force exerted by the air on a moving object, does come into play during the fall of a raindrop. However, in the case of a small raindrop, the effect of air resistance is relatively small compared to the force of gravity. This means that the raindrop's speed increase due to gravity outweighs the slowing effect of air resistance, leading to an overall increase in speed.

Regarding the other options:
- Option 2, its speed increases due to air resistance: While air resistance does act on the raindrop, it doesn't cause its speed to increase. Instead, air resistance tends to oppose the motion and can slow down the raindrop's descent.
- Option 3, it moves at a constant speed: This is incorrect because, as mentioned earlier, the raindrop's speed increases due to gravity.
- Option 4, it moves at a constant velocity: Velocity is a vector quantity that includes both speed and direction. In the case of a falling raindrop, its velocity is changing because the direction is constantly downward. Therefore, it does not move at a constant velocity.

By understanding the concept of gravity and how it affects the motion of objects, we can determine that option #1 is correct.