Question

the passage below describes an experiment.
a fish tank with snails
janelles manager at the pet store asked her to determine how to best keep algae off the walls of the fish tanks. janelle prepared six 20-gallon fish tanks, each with three goldfish. she added 10 snails to two of the tanks, 20 snails to two other tanks, and left the goldfish alone in the final two tanks. she observed the rate of algae growth in each tank.
in this experiment, the tanks with goldfish and ten snails were part of ____________.
an experimental group
a control group

Explanation:

In an experiment, experimental groups are exposed to the variable being tested (here, the number of snails, which is the variable for algae control). The control group is the untested baseline (tanks with only goldfish). The tanks with 10 snails receive a test variable, so they are experimental.

Answer:

an experimental group