Answer
a) red, blue, purple
b) #4
c) Nerve: orange, blue, green, black
Muscle: red, black, purple, blue
Work Step by Step
To get this answer, the most important idea is that all proteins for interacting with enhancers must be present for expression. Look for all x's or all dots to see which ones are needed or will be expressed in a) and b). For c), look for all of the elements present in the genes listed for each tissue.
