“Plant growth is dependent on the amount of fertilizer applied.” That was the hypothesis Mel and Bill decided on for their science project. They planted identical seeds in the same potting mix, and they used identical pots for each plant. Each pot received the same amount of water, and all the pots were placed in the same location in the greenhouse. After three weeks, Mel and Bill were able to summarize their data. Based on the data collected, what would be the MOST appropriate research question for further study?