The correct answer is A. "To err is human; to forgive is divine."
Explanation:
In grammar, an infinitive includes the preposition "to" and a verb in its bare form, for example, "to cook", "to live", etc. Additionally, infinitives can be used as subjects if these are the entities that perform the action or the entities described using a linking verb, for example, "To cry is useless".
According to this, the sentence that includes an infinitive as a subject is A. "To err is human; to forgive is divine" because in this the infinitives "to err" and "to forgive" are the entities described by the linking verb "to be" and therefore the subject in two different sentences.
