The squirrel reached for the birdfeeder, for he saw it was filled with an abundance of sunflower seeds.

the word for in the sentence is used as both

a. a gerund and an adverb
b. a noun and an adjective
c. a preposition and a conjunction
d. a verb and a demonstrative article

C) A preposition and a conjunction.

Explanation: a preposition is a word governing, and usually preceding, a noun or pronoun and expressing a relation to another word or element in the clause. A conjunction is a word used to connect clauses or sentences or to coordinate words in the same clause. In the given sentence, the word "for" is used as a preposition in the phrase "for the birdfeeder" and as a conjunction in the phrase "for he saw it was filled with an abundance of sunflower seeds."

i suggest it is anadiplosis