'de la quien' is correct... but 'de que' isn't?

Question

Hola InmaIn this test question: "Aquella chica del colegio, ________ todos se reían, estaba siempre triste"I managed to get all these correct: de la que, de quien, de la cual. But my answer de que was incorrect.OK, I admit that I did follow a pattern here and guess that this question required 'de' in front of the pronoun, so I actually have two questions about this:1) why is 'de' required in this particular structure (but not usually)?2) why is 'de que' incorrect? (but all the others require 'de')I ask because I don't see any reference to these nuances in the above lessonSaludos

Accepted Answer

Hola Graeme
1/ "de" is required here because it's using "reírse de alguien" that requires that preposition. So, when you laugh at someone you need "de". It's away from the verb because it's a subordinate clause and we place prepositions at the beginning: la chica de la que todos se reían.. (in English the preposition goes at the end: the girl they all laughed at...)
2/  with relative clauses using prepositions, you can sometimes omit the article with the relative "que", for example "con que..." "de que..." "en que":  los cuadros con [los] que decoramos la casa..., la tienda de [la] que te hablé...,  el lugar en [el] que nos conocimos... However, and this, I would need to check if it applies 100% of the time or it's just a tendency, when the referent is a person, we don't normally omit the article; it would sound odd/incorrect to say for example: "el hombre de que teníamos miedo... (the man we were scared of), los estudiantes en que confiamos... (the students we trust)... And this is the case in your sentence "Aquella niña del colegio, de la que todos se reían..." (de que todos se reían...???)
You can see lots of examples here in these other two lessons with relatives using prepositions:
Using preposition [except a and de] + el que, la que, los que, las que = with/for/on/in/from which (relative pronouns)
Using preposition a and de + el que, la que, los que, las que = to/of/from/about which/who (relative pronouns)
There is also a very informative article here from the site español avanzado that goes into detail on this topic (not an easy one...) 
I hope it helps.
Saludos y buen fin de semana.
Inma

Answer

Hola de nuevo Graeme
I forgot to say that the relative "quien" can never take the article, used with or without a preposition. For example:
La mujer para quien trabajo es muy simpática.
El chico con quien salí el sábado me ha llamado dos veces.
Aquellos empleados en quienes ponemos nuestra confianza recibirán un incentivo.
It'd be incorrect to say  "para la quien", "con el quien", "en los quienes"
 
 
I haven't found any example like the one you mentioned: 
"Aquella chica del colegio, de la que todos se reían, estaba siempre triste." in the lessons that we have for this topic.
If you tell me where you saw it, I can double check and make sure that all the correct/incorrect answers are set properly.
Inma