Given a scientific question, generate a correct answer to it.

Example input: Who proposed the theory of evolution by natural selection?
Example output: darwin
Example explanation: This is a direct fact that Charles Darwin proposed the theory of evolution.
Q: The rate of evaporation depends only on the surface area of the liquid and is essentially constant. the rate of condensation depends on the number of molecules in the vapor phase and increases steadily until it equals the rate of this?
A:
evaporation