William is testing what type of light best bean plants grow. he plants four beans in four separate pots. he places each pot in a different room and subjects them to different types of light, and he waters each plant the same amount. he uses sunlight, ultraviolet, fluorescent, and black light. william then measures the height and growth rate of each plant. which light source is part of the control group for william’s experiment? a) sunlight b) ultraviolet c) fluorescent d) black light