Los profesores les (dar) la tarea a sus estudiantes.

Explanation:

The right answer is LOS PROFESORES LES DAN LA TAREA A SUS ESTUDIANTES.

We need to remember that the Spanish language has specific grammatical rules that we have to follow to produce grammatical sentences without mistakes:

In our specific exercise, we need to conjugate the verb according to the subject, the direct and the indirect object. At this respect we have that:

So, now we know that the OBJECT PRONOUN “LES” Is needed because it refers to the plural indirect object “SUS ESTUDIANTES”.

OBJECT PRONOUNS are those words that always appear with a CONJUGATED VERB. They, as the PERSONAL PRONOUNS are in the place of a noun; their specific function into the sentence is to be the complement of the verb that they’re accompanying.

So, following the rules we can say that the correct option is to conjugate the verb in: SIMPLE PRESENT