TSA CBT Practice Test 2026 – The Complete All-in-One Guide for Exam Success!

The correct answer indicates that an infinitive appears as "to" immediately followed by a verb. This construction is a fundamental aspect of infinitives in English grammar. For instance, in the phrase "to run," "to" functions as the marker, and "run" is the base form of the verb. This structure allows infinitives to act as nouns, adjectives, or adverbs within a sentence, creating a versatile tool for expression.

The other options incorrectly identify how infinitives are formed or placed within a sentence. An infinitive cannot be formed with a gerund (a verb ending in -ing), nor can it immediately follow a noun in a way that would create a valid infinitive phrase. The structure where "to" appears at the end of a sentence does not conform to the typical usage of an infinitive, as it does not convey the action or state associated with it. Therefore, the recognition that infinitives consist of "to" plus the base form of a verb is crucial for understanding their function in a sentence.