Question

select the part of the subject that agrees with the bold verb. the squirrels that live in ned flanderss tree house have collected nearly 300 acorns.

Explanation:

The verb "have collected" is plural. The subject - "the squirrels" is plural and agrees with the plural verb. The relative clause "that live in Ned Flanders's tree house" is just additional information about the squirrels.

Answer:

The squirrels