First Mate:Captain, our journey thus far has taken many detours

Captain's plan: I’ll slightly reduce our speed for the rest of the way to conserve fuel.
Goal of the plan: Conserve fuel to make it home today.

Perhaps the Captain is trying to avoid detour for re-fuelling by conserving fuel and thereby planning to reach today.

Look for an option that explains why reducing speed may not conserve fuel and lead to home today.

A)His ship has already averaged a much slower speed than it had planned for, and so the passengers will be disappointed with their late arrival.
The plan is not to avoid passenger disappointment. Irrelevant.

B)The last leg of the journey is known to be the most treacherous leg of the trip.
Irrelevant. If it is known, it must be included in the timeline.

C)There are no fueling stations between the ship’s current location and its destination.
It doesn't matter whether fueling stations are there. The captain is trying to avoid the need to re-fuel.

D)Rate of speed is not a substantial determinant of the amount of fuel a vessel uses.
Even if speed is controlled, not much fuel will be saved. So then the plan may not succeed.

E) Regardless of the rate at which the captain travels for the remainder of the trip, the ship will not come close to making its predicted arrival time.
The point is not to make the "predicted arrival time". The plan is to make it home today. Whatever delays have happened, have happened. Now the plan is to make it home today.

Answer (D)