A scientist wanted to study the effect of a drug on the blood pressure of rats. She set up an experiment in which the experimental group consisted of rats that were injected with a salt solution containing the drug. What should the control group have consisted of?

The control group would not receive any medication or they would be given the salt solution without any drugs with it (basically a placebo).

A dependent variable is a variable dependent on another variable: the independent variable. In simple terms, the independent variable is said to cause an apparent change in, or simply affect, the dependent variable.

The variables you have are what the rats are feed (their diet), number in cage, size of the cage (things such as a smaller care with more within it should cause undue stress), what they are exposed to within their environment. Even things sun as amount of light within the room, the temperature of the room, etc.