Which of the following is NOT an example of an introductory word?

The correct choice identifies "that" as not being an example of an introductory word. Introductory words typically serve to connect thoughts, provide context, or signal transitions in a piece of writing. Words like "however," "although," and "since" are commonly used at the beginning of sentences to introduce contrasting ideas, conditions, or reasons.

"However" is often employed to indicate a contrast with the previously mentioned idea. "Although" introduces a subordinate clause that presents a condition contrary to what might be expected. "Since" indicates a reason or basis for what follows. In contrast, "that" is often used as a relative pronoun or a conjunction within a sentence rather than functioning to begin one. It does not serve the same introductory purpose as the other words listed, which is why it is the correct answer in this context.