In a balanced ecosystem, the number is far greater than the number .
first blank: (producers, tertiary consumers, herbivores)
second blank: (consumers, omnivores, secondary consumers)

Producers / Consumers

Explanation:

From ody ssey assignment 6 page 8 (if printed) under Balance of Nature.

sentence number 1 "In a balanced ecosystem, the number of producers is far greater than the number of consumers.

well, that's easy; the answer's c, "it reduces contamination of the water and substrate of the estuary."