Which of the following pairs represents antonyms?

The pair of words "bad and good" represents antonyms because they express contrasting meanings. "Bad" conveys something negative, undesirable, or of poor quality, while "good" signifies something positive, desirable, or of high quality. This clear opposition in meaning establishes them as antonyms.

In contrast, the other pairs do not represent antonyms. For example, "happy and joyful" are synonyms that describe similar states of feeling. "Hot and warm" indicate temperatures that are related but differ in intensity, with neither being a direct opposite of the other. Similarly, "fast and quick" both pertain to speed, again highlighting a similarity rather than opposition. Thus, the relationship between "bad" and "good" stands out as the only true antonym pair in the options provided.