Final answer:
The independent variable in Lauren's experiment with African violets is the location of the plants in her apartment.
Step-by-step explanation:
In the experiment described by Lauren, the independent variable is D. The location of the plants in the apartment. The independent variable in an experiment is the factor that is changed or manipulated by the researcher to observe its effects on the dependent variable, which in this case would be the growth or health of the African violets.
Lauren has controlled the other potential variables by ensuring each African violet has the same size pot, the same type of soil, and receives the same amount of water. Therefore, variations in the growth of the African violets can be attributed to the difference in their locations, which is the independent variable.