Question

Frank is doing an experiment to find out how the amount of oxygen dissolved in water affects the growth of algae in a body of water. He dissolves different amounts of oxygen in ten otherwise identical samples of water.
What should Frank do next?
Place each sample of water in a freezer, and measure the temperature at which each freezes.

Add a pair of minnows to each sample of water, and measure the rate at which they reproduce.

Carefully bring each sample of water to a boil, and measure the temperature at which each boils.

Add equal amounts of algae to each sample of water, and measure the rates at which they grow.

Answer 1

Answer:

The correct answer is "Add equal amounts of algae to each sample of water, and measure the rates at which they grow."

Explanation:

Frank's experiment is designed to determine if the amount of oxygen dissolved in a sample of water affects the growth rate of algae in the water. To do this, he should add equal amounts of algae to each sample of water and measure the rates at which they grow.

Answer 2

Since the experiment is studying the growth of algae.  The only step that makes sense is putting in equal amounts of algae to each sample of water.  All of the other steps are testing different ideas.  For example placing the samples in a freezer to see what the freezing point is is testing how the amount of oxygen in water affects the freezing point of water.