Identify the non-finite verb forms in this sentence: 1. She was looking for her sister.

Looking (#1)

Explanation:

Non-finite Verb

Non-finite verbs function as nouns, adjectives, or adverbs or combine with a finite verb for verb tense. Non-finite verbs Include participles, Infinitives, gerunds, other verbs that don't change form when the subject changes.

Participle

A verbal that is used as an adjective, describes a noun or pronoun, present participles always end in -ing, past participles usually end in -ed.

Gerund

verb form acting as a noun - always ends in -ing.

Infinitive

a verb form that is used as a noun, an adjective, or an adverb and is typically preceded by the word to.

Continuation:

Word: She (Pronoun)

She is a pronoun. It's a noun that refers to another noun or noun phrase anaphorically, although it can't be preceded by a determiner and seldom accepts an attributive adjective. In English, examples are I, you, he, who, me, mine, and so on. It can also be used as a subjective or nominative pronoun. It is most commonly used to begin a statement. It is, however, rarely used as a noun.

Word: Was (Linking Verb)

The word "was" is a verb, more precisely a linking verb, since it connects the subject to the section of the sentence that offers further information about the topic. Furthermore, this form of the verb "to be" represents a state of being.

Word: Looking (Present Participle)

Looking is the present participle of look. A participle is a verb that ends in -ing (present) or -ed, -en, -d, -t, -n, or -ne (past) and serves as an adjective, modifying a noun or pronoun. A participial phrase is made up of a participle and one or more modifiers, objects, and/or complements (s).

Word: For (Preposition)

When used to signify the usage of something, the place where an object or person is going, or the period of time, the word "for" is defined as a preposition.

Word: Her (Pronoun)

Her is a pronoun in the third person singular. Her is the subject or object of a verb or a preposition. Her is a possessive determiner as well. You refer to a lady, a girl, or a feminine animal with her.

Word: Sister (Noun)

This word is referring to someone's/something's female sibling. This word is a noun because a word that is a person, place, or thing is classified as this part of speech. The noun sister can be used as either a proper or common noun. After looking through this sentence, we can come to one conclusion. Since looking ends in -ing, it is classified as a gerund. Therefore, the word looking is a non-finite verb.

All the other words in the sentence are not considered or classified as non-finite verb as their word classifications do not match those of the description/definition given of what a non-finite verb is.

She was looking for her sister.

NOTE:  Verbs with tense are finite, and verbs without tense are nonfinite.