Please help <3 Read the following scenario and state which of the following could be a control group?

I have noticed that in my garden the bean plants that are growing in one area are taller than the bean plants growing in a different area. I think the beans are taller because that area of the garden gets more light than the other area. I have decided to conduct an experiment to see if the amount of light influences bean height.

changing the type of light

changing the type of bean plants

changing the unit of height measured

using no light