Janine wants to answer a question about how fertilizer affects the growth of her corn plants. She adds the fertilizer to half the plants in her cornfield. Which option describes the best data she can collect to help her draw a conclusion about the effect of the fertilizer on the corn?

A. the weekly rainfall for a month

B. the height of each corn plant each day for a few weeks

C. the temperature each day for a few weeks

D. the cost of the new fertilizer compared to the old fertilizer