Provide your best answer for the following question. Give ONLY the answer, no other words or explanation.
For example:

Answer: <most likely answer, as short as possible; not a complete sentence, just the answer!>.

The question is: Nicole was studying different ecosystems. She compared the number of plants living in a forest to those in a desert. Which factor best explains why more plants may survive in a forest?
There is more rain in the forest.
Rainfall.