Which of the following is an example of a modal auxiliary verb?

• A. might
• B. quickly
• C. suddenly
• D. really

Answer: (A)

Modal auxiliary verbs express mood such as possibility, necessity, or permission and sit with the base form of a main verb. In this case, might is the modal that signals possibility, as in "She might go," where it stays before the base verb without changing for subject. It shows uncertainty about what could happen, rather than describing how something happens or modifying an adjective.

The other words are adverbs. Quickly indicates speed or manner, suddenly signals a rapid change or event, and really acts as an intensity booster for adjectives or other adverbs. They don’t function as auxiliary verbs that modify the main verb's mood, so they’re not the correct type in this context.