4. In his science fair project, Julio did the following: He took 4 fish tanks and put 10 fish of identical size in each. Fish in tank 1 received 4 hours of light/day, fish in tank 2 received 6 hours of light/day, fish in tank 3 received 8 hours of light/day, and fish in tank 4 received 12 hours of light/day. At the end of 2 months, he measured the size of all fish and compared the fish in tanks 1, 2, and 3 with the fish in tank 4 because fish in tank 4 received the amount of light recommended by his teacher. what is the control?