How is the conjugation of a verb determined?

The correct choice is based on the understanding that the conjugation of a verb in Latin is typically determined from the second principal part, which is the infinitive form of the verb. The infinitive provides critical information about the verb's conjugation class, including its endings and how it will change across different tenses, moods, and persons.

In Latin, verbs are grouped into four main conjugations, each characterized by specific patterns in their endings. The second principal part, often the infinitive, reveals not only the verb's conjugation but also helps in forming other forms of the verb, such as the present, imperfect, and future tenses. This is fundamental in learning how to properly conjugate verbs, as it serves as the reference point for building the verb's various forms.

The other choices do not serve as the primary basis for determining verb conjugation. The first principal part, while useful for identifying the first person singular present form of the verb, does not provide sufficient information about its conjugation class. The past participle is often used in perfect tenses and passive forms but does not indicate the overall conjugation. The subjunctive mood refers to a specific verb form and does not help in categorizing the verb's conjugation.