c) urged
In this sentence, exhorted is the action of the elder traveler. The use of the word "onward" suggests that the people have been traveling a long distance and still have a long distance to go. We also know that the elder wants the other traveler with him "to make good speed" or hurry up. Since exhorted is a verb, we need another verb to act as a synonym. Worthy is not a verb so it is eliminated immediately. Also, helped can be easily eliminated because the story does not make either person sound as though they'd be generous or helpful. The elder traveler does not sound as though he would not beg for anything. The correct answer is urged.
