A certain large pond had many plants growing in it. It also had a population of fish living in it. One day, a chemical spilled i
nto the water. This chemical caused the plants to die. A scientist monitored the pond after the chemical spill. She found that the amount of dissolved oxygen in the pond gradually decreased. Once it reached about half of its original amount, the fish in the pond began to die.
Which statement best explains this information?
A. Fish produce oxygen through respiration, and this oxygen is used by plants.
B. All the oxygen in a pond comes directly from the atmosphere, so fish do not need plants.
C. Plants produce oxygen through photosynthesis, and fish depend on this oxygen to survive.
D. Fish and plants compete with each other for the dissolved oxygen in a pond.
