There are elements of truth in each of the options, but C is the only correct answer.
While Ben Gunn hints to Jim that he has already found the treasure, claiming that he's rich, Jim doesn't catch on to this at the time. Because Jim left the stockade to recover and beach the Hispaniola, he wasn't present to learn Dr. Livesey negotiated with Ben Gunn to relocate the stockade group to Gunn's cave, where...
To make it parallel I would say to put it in this format: We can’t go back; to go forward is our only option. This makes the verbs the same.
C. clear thesis, a short outline, and a strong conclution
