Official Explanation
John assumes that his round-trip driving time between the two towns will be similar to XYZ’s average time, over the last five years, for the same round trip. Therefore, John’s conclusion will be weakened by (a) any systematic difference between John’s personal trip and XYZ’s company trips, or (b) any reason why the five-year average is not representative of the time currently required to drive between the two towns.
(A) If this statement is true, then the five-year average commute time will not be representative of the current commute time, since the increasing congestion will have raised the current commute time to a level greater than the five-year average.
(B) If most of XYZ’s courier vehicles are subject to speed limits lower than those for commuter automobiles, then the courier vehicles’ commute time will probably be longer than John’s commute time in his personal vehicle.
(C) Correct The cited round-trip time specifically excludes the time required for loading, unloading, and delivery, so the length of time taken by these tasks is irrelevant to the conclusion at hand.
(D) Since traffic patterns are highly dependent upon the time of day, the given 80-minute average cannot necessarily be expected to hold at times when XYZ does not make deliveries.
(E) If this statement is true, then, for the first three years of the five-year period in question, the transit time between the two towns would have been much longer than that for the last two years of the period (and thus the current time). Therefore, in this case, the five-year average will not be representative of the current time.
The correct answer is C.