Error in sequence to tense. This sentence illustrates the use of the future prefect tense. The present perfect tense, as used in Choice A, and the past perfect tense, as used in Choice B, are incorrect. Choice C correctly indicates that an anticipated event will be completed before a definite time in the future. Choice D is weak because of the used of passive voice and the consequent vagueness as who is performing the action. Choice E is awkward because of the needless separation of subject (we) from verb (shall have traveled).
Answer: C