("That man was lying when he said that in the real life program")
Ese hombre estaba _MINTIENDO__ cuando dijo eso en el programa de vida real
It's the imperfect progressive verb tense... when you describe a situation/context of part punctual action.
The other possible answers are also conjugations of the verb mentir.... but non of which goes with the "estaba" (to be) part, since "estaba" calls for the present participle (mintiendo).
