An experiment is done on three tomato plants over a 50 day period to test the following hypothesis: If either fertilizer or compost is used on plants then a plant that gets fertilizer will affect the plant growth the most. The same amount of water and light were applied to each tomato plant. Pot A contained no fertilizer or compost, Pot B contained fertilizer and Pot C contained compost. Which is the independent variable? a. Time of experiment b. Amount of water c. Plant growth d. Amount of fertilizer