Adependent variable is best described as a. the variable that causes other variables to change. b. the variable that must be kept from changing. c. the variable that responds to changes in an independent variable. d. the variable that determines which other variables will be independent.

The answer is c. A dependent variable relies on the independent variable. If the independent variable changes then, the dependent variable will change also.
For example:
A scientist is studying how the amount of water you put into a plant affects plant growth.
Dependent variable: plant growth
Independent variable: amount of water

That would be a working theory.