A biologist listens to frogs singing at a local pond and hypothesizes that the sounds may be mating calls. What would be the next step?

The correct answer is - make a prediction

Explanation:

A hypothesis can be defined as an explanation of any observation which can be confirmed by experiments and prediction is the guess about the future result of any observation.

As here a biologist hypothesized that the sound produced by frog is mating calls than the next step of the biologist would be to make a prediction about response of that mating call by female frogs. This is called hypothesis prediction method.

Therefore the right answer is - biologist will make a prediction.