In which verbal operant does a speaker respond to a verbal prompt by repeating what was said?

The correct answer is the echoic verbal operant because it specifically involves a speaker responding to a verbal prompt by repeating what was just said. In echoic behavior, the speaker's response is a direct imitation of the verbal stimulus they heard, which is often characterized by the same phonetic sounds as the prompt. This operant is crucial for language development, as it reinforces verbal skills through imitation.

In contrast, the other verbal operants have different functions. A mand involves a request or demand for something that the speaker wants. A tact refers to labeling or naming an item or event based on the speaker's observations, and a textual operant involves reading written words or text aloud. Each of these has its unique role in communication and language acquisition, differentiating them from the repeat-response nature of echoics.