Explanation:

When determining whether to use the adjective "angry" or the adverb "angrily" in this sentence, we need to consider the function of the word in the sentence and the context in which it is used.

Adjective vs. Adverb:
- Adjectives describe or modify nouns, pronouns, or other adjectives. They provide more information about the noun or pronoun they are modifying. Examples of adjectives include "angry," "happy," "tall," etc.
- Adverbs, on the other hand, describe or modify verbs, adjectives, or other adverbs. They provide more information about the action or state expressed by the verb or adjective. Examples of adverbs include "quickly," "happily," "loudly," etc.

In the given sentence, we are describing how he looked at me when I interrupted him. The word "looked" is a verb, so we need an adverb to describe how he looked.

Function of the Word:
- The word "angry" is an adjective. If we use "angry" in the sentence, it would modify the pronoun "he" and indicate that he is angry.
- The word "angrily" is an adverb. If we use "angrily" in the sentence, it would modify the verb "looked" and describe the manner in which he looked at me.

Context:
- The sentence states that he looked at me when I interrupted him. It implies that his look was a response to the interruption, suggesting that he may have been irritated or displeased.
- The adverb "angrily" aligns better with the context of the sentence, indicating the manner in which he looked at me in response to the interruption.

Correct Answer:
Therefore, the correct answer is "angrily" because it is an adverb that appropriately describes the manner in which he looked at me when I interrupted him.