The correct answer is C. Melanie was riding her bicycle all afternoon.
Explanation:
In grammar, the past progressive tense is a type of tense that refers to an action that occurred in past but was in progress during a specific time, this tense is used to show one action that was occurring and then this was interrupted by other or because the action described did not end immediately. Because of this, in sentences that use past progressive tense, the verb is formed by the word was/were depending on the subject and a verb ending in -ing or present participle. Therefore, the sentence that uses past progressive tense is "Melanie was riding her bicycle all afternoon" because this is the only sentence in which the verb is formed by the word "was" followed by a present participle "riding", also this sentence describes an action that did not end immediately in the past.
