Answer: Percolation
Explanation: It is the ability of water to sip in into the ground. Percolation is the process wherein the ground absorbs water up to the amount it can hold. When the soil or ground is saturated with water it loses its ability to absorb water and causes it to run off. Unsaturated ground can absorb more water through percolation process.
Answer:
Populations have variation in traits due to random mutation, crossing over and environmental conditions.
It should be natural selection since there is no external influence implied. (like environment or genetic mutations.)
