Una respuesta está en la gran diversificación de las actividades humanas y sociales que, __________ (impulsar) a los ecuatorianos a ingresar, más temprano que tarde, a un proceso de especialización laboral, que antes ni siquiera se analizaba.
I initially put impulsada (referring to diversificación), but my teacher said it cannot be this because a) impulsar would take hacia, not a, and b) the que is introducing a relative clause which adds "additional information" and so you must conjugate the verb (she said the answer was impulsan). Now, I get that my answer was wrong and understand what she's trying to say about the relative clause, but my problem was that comma after que, which is what initially led me to use a participle there. I was willing to accept her answer and figure that the comma was a typo in the book, but she said that it was fine with the comma. I think that would be a run-on sentence (and even more ungrammatical when you go farther in the sentence). Can you put a comma here in Spanish?
Also, when I mentioned that que was a relative pronoun in this case, she said it wasn't, that it was a conjunction. I'm pretty sure it's a relative pronoun. Who's right?
I hope all that was comprehensible. Funnily enough, I get very fragmented and difficult to understand when writing about grammar!