The word for in the sentence is used as both
the squirrel reached for the birdfeeder, for he saw it was filled with an abundance of sunflower seeds.
a.) a gerund and adverb
b.)a noun and adjective
c.) a preposition and conjunction
d.)verb and demonstrative article

C) A preposition and 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. The word "for" can be a preposition or a conjunction. In the given sentence it is a preposition when used in the phrase "reached for the birdfeeder" and it is a conjunction joining two clauses in the phrase "for he saw it was filled with an abundance of sunflower seeds."

a is is the correct answer