The sentence that contains a participle functioning as a verb is:
The blinking sign warns drivers of a sharp curve ahead.
In this sentence, "blinking" is a present participle used to describe the sign, but the primary focus here is the verb "warns," which is the main verb of the sentence.
However, since all options have slight confusion in their phrasing, the correct respuestas bearing participles as adjectives include "blinking," but "waiting" in the first sentence also serves a participial role as a part of the verb phrase.
Given the specific request, if looking strictly for a participial form acting primarily in establishing the action, then the first sentence "The students are waiting for the bus," with "waiting" acting as part of a progressive verb form, may be a point of contention.
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