what is the part of speech of this sentence?

8. She is a terrible teacher.
adverb
interjection
verb
adjective

I'm stuck between interjection and adjective?

Sentences are not a part of speech. Only words are parts of speech.

http://www.enchantedlearning.com/grammar/partsofspeech/

Please do not post any more of these questions until you've studied the above site.

the function of the sentence****** ?

It's a declarative sentence.

http://www.infoplease.com/cig/grammar-style/sentence-functions-four-tops.html

To determine the part of speech of a word in a sentence, you need to understand the function it serves within the sentence. In this case, let's break down the sentence and analyze the possible options:

1. Adverb: Adverbs usually modify verbs, adjectives, or other adverbs. They answer questions such as how, when, where, or to what extent. In the sentence "She is a terrible teacher," there is no adverb modifying any word.

2. Interjection: Interjections are words or phrases that express strong feelings or emotions. Examples include words like "Oh," "Wow," or "Yuck." In the given sentence, nothing exists that would classify it as an interjection.

3. Verb: A verb is a word that describes an action, occurrence, or state of being. In the sentence, the word "is" is a linking verb, which connects the subject "She" to the subject complement "a terrible teacher." Therefore, "is" is not the part of speech that we're trying to identify.

4. Adjective: Adjectives describe or modify nouns or pronouns. They provide more information about the noun or pronoun they are attached to. In the given sentence, the word "terrible" is describing the noun "teacher." Thus, "terrible" is an adjective.

Therefore, the correct answer is adjective.