A student set up a small freshwater fish tank. The tank included water, fish, gravel, a snail, and plants, as represented below. Which statement best describes an activity performed by a student investigating an abiotic factor using this setup?

A) He records the temperature of the water.
B) He feeds the fish 0.5 gram of fish food twice a day.
C) He measures the growth of the plants with a metric ruler.
D) He observes the snail scrape algae off the gravel.