trey is conducting an experiment to determine which fish food causes the most goldfish activity over a period of two weeks. he is going to set up ten fish tanks with 4 goldfish each. he will feed the fish in half of the tanks swift salmon food and the fish in the other half of the tanks fast flounder food. he will expose them to direct sunlight for 4 hours per day. each tank will have the same size and type of goldfish, which will be fed the same amount of fish food. each tank will be filled with the same type and amount of water and with the same type and amount of river rock.

which change would be the most effective way to improve the validity of this experiment?
a) increase the number of goldfish in each tank.
b) increase the daily amount of food for each tank.
c) create another group that is fed regular fish food.
d) increase the number of tanks in each treatment group.