Final answer:
Option d) Apollo, unused to rejection, sank down on his knees beside the tree and the river where he stayed a long, long time. has the best parallel structure.
Step-by-step explanation:
The best sentence that applies parallel structure to the combined sentences from the given excerpt is option d) Apollo, unused to rejection, sank down on his knees beside the tree and the river where he stayed a long, long time. Parallel structure involves using the same grammatical form or structure in a series of words, phrases, or clauses. In this sentence, all the verbs are in the past tense and have a similar structure: sank, stayed.