1. Estudia para el examen.
2. No olvides mi cumpleaños.
3. No digas nada.
4. Pregúntale al profesor.
5. Sean buenos amigos.
Number 2! (Nosotros vemos las manzanas). The first one is conjugated to the 'yo' form, the third is conjugated to the 'el/ella' form, and the fourth is conjugated to the 'ellos/ellas/ustedes' form, which is wrong for the sentences.
David y roberto '''son''' buenos amigos
