Which of the following sentences contains an infinitive verb form used correctly in standard English grammar?

Introduction / Context:
This sentence based question tests knowledge of infinitive verbs in English grammar. An infinitive is the base form of a verb that is often introduced by the word to, such as to go, to eat or to make. Recognising infinitive constructions is important for understanding sentence structure and verb usage in competitive examinations and language learning.

Given Data / Assumptions:

Option A: We walked to town with Grandfa.
Option B: It is normal to make mistakes.
Option C: Will you take the package to Sheila?
Option D: None of the above.
We must identify the sentence that clearly contains an infinitive verb form.

Concept / Approach:
An infinitive usually appears as to plus the base form of a verb, for example to make. It does not show tense and often acts as a noun, adjective or adverb in a sentence. The key is to distinguish between to used as part of an infinitive and to used as a preposition indicating direction or relationship, such as in to town or to Sheila. Only a true to plus verb combination counts as an infinitive.

Step-by-Step Solution:

Verification / Alternative check:
Another way to verify is to try replacing the suspected infinitive phrase with a gerund like making. In sentence B, It is normal making mistakes sounds ungrammatical, confirming that we need the infinitive to make. In sentences A and C, replacing the preposition to with a gerund plus object does not produce a meaningful verb phrase, which further shows that there is no infinitive there. This reinforces that to make in sentence B is the only proper infinitive present in the options.

Why Other Options Are Wrong:

Sentence A uses to as a preposition showing direction towards town, not as part of a verb.

Sentence C uses to as a preposition indicating the recipient Sheila, again not forming an infinitive verb expression.

None of the above is incorrect because sentence B clearly contains a valid infinitive structure.

Common Pitfalls:
Many learners assume that any appearance of the word to automatically signals an infinitive, which is not true. The word to can act as a preposition, and only when it is directly followed by a verb in base form is it part of an infinitive. Careful reading and recognition of whether to is introducing a verb or a noun phrase are essential to answering questions of this type correctly.

Final Answer:
The sentence that correctly contains an infinitive is It is normal to make mistakes.