Question

They look tired and should rest if they_________ (work out).

Answer 1

Respuesta:

They look tired and should rest if they have worked out.

They look tired and should rest if they are working out.

They look tired and should rest if they will work out.

Explicación:

Lo escribí en los tres tiempos (Orden: Pasado primero, presente segundo y futuro tercero.) ya que no explicaste que había que hacer, espero que te sirva.