Question

select the pronoun whose antecedent is flax seeds. how many bags of flax seeds did you buy? i know they are a great source of fiber, but are twelve bags really necessary?

Explanation:

To determine the pronoun with the antecedent "flax seeds", we analyze the sentence. In "I know they are a great source of fiber...", "they" refers back to "flax seeds" (the antecedent) as "flax seeds" is a plural noun and "they" is a plural pronoun used to refer to it.

Answer:

they