What is the only verbal operant that directly serves the speaker?

The correct choice is the mand, as it is a type of verbal operant that directly serves the speaker's needs or desires. When a speaker uses a mand, they are specifically requesting something they want, which makes it a unique form of communication focused on fulfilling their own needs. For example, if a child says "juice," they are asking for juice because they are thirsty. The mand prompts action or an answer that satisfies an immediate need or want of the speaker.

In contrast, the tort conceivable between the other verbal operants lies in their functions. A tact involves labeling or describing an object or event in the environment, which primarily benefits the listener by providing information. An echoic is a verbal response that is a direct repetition of what someone else said, serving primarily as a learning tool rather than fulfilling a need of the speaker. Intraverbals are verbal responses that are not tied to a direct request, often answering questions or engaging in conversation, which again serves more to facilitate interaction than to fulfill the speaker's immediate desires. Thus, the mand stands out because it directly addresses the needs of the speaker, making it the only verbal operant that serves that purpose.