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.