A biology student wanted to study the effect of fertilizer on the growth of tomato plants. He placed four of the same type of tomato plants into separate containers, each containing the same amount of soil. Each pot received a different watering solution, containing varying amounts of fertilizer. The table below shows the average height of the plants by the end of one week.
Plant group Fertilizer amount (g) Avg height of plants (cm)
1 0 3.0
2 5 3.2
3 10 4.4
4 20 5.0

A. The height of the plants

B. The amount of fertilizer

(Choice C)

C. The type of tomato plant

D. The amount of soil provided