I think the answer is:
B) oceanic crust-continental crust
If it's not falling through air, water, smoke, or anything else,
and gravity is the only force on it, then its speed increases
at a constant rate ... 9.8 meters per second for every second
it falls. (That's the number on Earth. It's different in other places.)
1. First answer
2. Troposphere
3. Rotation
4. Humidity
5. Barometer
The most appropriate answer is C !! the Sun !!