TASK DEFINITION: In this task, you are given a question and an answer, you would be asked to create the sentence based on the Question-Answer provided. It should be contained within the Question-Answer provided.
PROBLEM: Question: What is the unit of evolution? Answer: population

SOLUTION: Population is the unit of evolution.

PROBLEM: Question: Water follows where sodium ions lead, due to what process? Answer: osmosis

SOLUTION: Water follows osmosis sodium ions lead, due to what process.

PROBLEM: Question: When light passes from one medium to another, it changes what? Answer: speed

SOLUTION:
When light passes from one medium to another, it changes speed.