An infinitive composes the words "to" plus the "simple verb". Infinitives can be used as nouns, adjectives or even adverbs. In the given sentence above, the part of the sentence that contains an infinitive is, "to enrich". The infinitive "to enrich" is used as an adverb in the sentence modifying the verb
"decided".
I believe the answer is C.
Beautiful is what I would say
Plants absorb food from the external environment