amount of agar amount of light amount of garlic amount of growth
I gave my students this multiple choice question: A student wants to determine the effect of garlic on the growth of a fungus species. Several samples of fungus cultures are grown in the same amount of agar and light. Each sample is given a different amount of garlic. What is the independent variable in this investigation?

Only one answer is correct among these 4 choices:
- amount of agar
- amount of light
- amount of garlic
- amount of growth

Could you tell me which one is correct?

amount of garlic