Answer:
Option C is the correct answer.
Step-by-step explanation:
Past progressive or past continuous is a tense used to express actions in progress in the past. It can be identified because a) it used the auxiliary be in past (was or were) and b) it requires the verb in its participle form, plus ing, such as write=writing.
Option C describes an action in progress (Melanie was riding) at a specific time in the past (all afternoon) so it is the correct answer.