Biology

A possible explanation for why something happens is called: a hypothesis.

Here's why:

A hypothesis is a testable explanation or prediction for an observed phenomenon. It's often based on prior knowledge, observations, or research, and it can be tested through experimentation or further observation.

The other options:

A.A variable: A variable is a factor or condition that can change in an experiment. It is not an explanation, but something that can be measured or manipulated in ...