'That' precedes the noun 'book' and points out specifically which book is being referred to. When a demonstrative word modifies a noun, it acts as a demonstrative adjective.

Reflexive pronouns end in -self or -selves and are used when the subject and the object of the sentence are the same. 'Myself' is a reflexive pronoun.

'Are' is a form of the verb 'to be'. In this sentence, it functions as a linking verb connecting the subject 'They' to the adjective 'happy'.

Coordinating conjunctions connect words, phrases, or clauses of equal rank. 'But' is one of the FANBOYS (For, And, Nor, But, Or, Yet, So) coordinating conjunctions.

A collective noun refers to a group of individuals or things. 'Team' refers to a group of players acting as a single unit.

Abstract nouns refer to ideas, qualities, or states rather than concrete objects. 'Happiness' is a state of being, making it an abstract noun.

A proper noun names a specific person, place, or organization and is always capitalized. 'London' is the name of a specific city.

In this context, 'hard' modifies the verb 'works', describing how he works. Thus, it functions as an adverb.

Here, 'hard' modifies the noun 'test', describing what kind of test it is. Therefore, it functions as an adjective.

Interjections are words or phrases used to express strong emotion or sudden feeling. 'Wow' expresses amazement and stands grammatically independent from the rest of the sentence.