Multiple choice:
¿qué oraciones contienen mandatos formales?

josé, vaya a clase.
catalina, practica el piano.
caben más libros en la caja.
niños, jueguen en el patio.
chicos, empiecen a leer la lección.

Explanation:

1.José, vaya a clase.

Jose, go to the class.

The verb we have here is to go, IR. In this case, the sentence we have here is in the third person singular form. But, it's not in the indicative. It's in the present, subjunctive tense, as this is an affirmative command in Spanish language. We use this type of command for our bosses, older people, or simply someone we don't know very well.

2.Niños, jueguen en el patio.

Kids, play on the playground.

The verb we have here is to play, JUGAR. In the given example, this verb is in the third person plural form. The verb is in present tense, but it's not in indicative, it's in subjunctive. We used this as a command, since we're ordering kids where to play.  This verb belongs to the first group of verbs, as it ends in AR.

3.Chicos, empiecen a leer la lección.

Guys, start reading a lesson.

The verb we have here is to start, EMPEZAR. The given verb is in the third person plural form. The verb belongs to the second group of verbs because of the AR ending. It is irregular. The verb is in present tense. It is not in indicative, it is in the subjunctive. The other verb we have is LEER, which means to read, it's in infinitive.