Read the following experiment and answer the questions. Mary had observed that bean plants seemingly grew taller when Fertilizer A was applied. She decided to conduct an experiment with bean plants to determine which type of fertilizer would produce the tallest bean plants in a 90 day period. She selected three courainers of the same exact size and placed the same amount of potting soil in each container. She placed 100 bean seeds in each of the three containers. Each seed was planted the same distance apart in each container. She placed all three containers on the covered back porch. She added FERTILIZER A to one container and FERTILIZER B to another container. SHE DID NOT FERTILIZE THE PLANTS in the third container. She watered the three containers of plants every other day for 90 days. She watered with the same amount of water and distributed the water evenly in each of the three containers. At the end of 90 days, the container of plants receiving FERTILIZER A produced plants with an average plant height of 17 inches. FERTILIZER B plants averaged 12 inches, and the container receiving no fertilizer averaged 10 inches in height. Name the independent variable.