Recently james noticed a strange smell coming from the water and noticed a large number of dead fish at the surface. he thought that a change in the environment was causing the fish to die. james asked the coast guard about the brownish red color of the water and discovered it was algae. james wondered if the alga was killing the fish. to test his idea, he collected water from the ocean area that was brownish red in color with high levels of algae, then went further north of his area and located water that did not appear to have the same algae. he also caught 12 small fish that appeared healthy from the northern area. james obtained three 30 gallon tanks and set each tank up properly.

tank 1: james placed 30 gallons of the water with no algae,
tank 2: he put 15 gallons of water with no algae and 15 gallons of water with algae
tank 3: he put 30 gallons of water with algae.
he placed 4 fish in each tank. after making careful notes every 3 hours, his results showed that after 72 hours, all fish in tank 2 and tank 3 were dead. no fish in tank 1 showed any signs of sickness.

if we wanted to know for sure that the algae was causing the fish deaths, what would need to be done with james' experiment?

a: nothing
b: continue observing the area
c: redo the experiment using the same variables
d: do a totally different lab experiment