Context: The passage below describes an experiment.

Zeke grew ten  on his back porch. He grew each plant in its own pot. Zeke noticed that his plants did not grow many leaves, and he wanted to see if earthworms could help them grow more.
Zeke divided his ten plants into two equal groups. He added three earthworms each to the soil in five of the pots. He did not add any earthworms to the other five pots. Two months later, he counted the number of leaves on each of the ten plants.
Figure: mint plants.
In this experiment, which were part of a control group?
A. the mint plants that did not get earthworms
B. the mint plants that got earthworms
Determine the correct option from the provided choices and reply with its corresponding letter.

A