Context: The passage below describes an experiment. Read the passage and think about the variables that are described.

Derek grew ten  on his back porch. He grew each plant in its own pot, and each pot was the same size and shape. Derek noticed that his plants did not grow many leaves, and he wanted to see if earthworms could help them grow more. To test this idea, Derek divided his ten plants into two equal groups. For one group, he added three earthworms to the soil in each pot. He did not add any earthworms to pots in the other group.
Two months later, Derek counted the number of leaves on each of the ten plants. He compared the number of leaves on the plants in each group.
Hint: An independent variable is a variable whose effect you are investigating. A dependent variable is a variable that you measure.
Figure: mint plants.
Which of the following was a dependent variable in this experiment?
A. the number of earthworms
B. the number of leaves
Select the correct answer from the provided options and reply with the letter associated with it.

B