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"A quién" is a phrase which is often translated as "to whom", and "por la que" is a phrase which is often translated as "by which". Learn more about the difference between "a quién" and "por la que" below.
a quién()
A phrase is a group of words commonly used together (e.g., once upon a time).
a. to whom
Si no sabe a quién dirigir la carta, llame y pregunte.If you don't know to whom you should address the letter, inquire about it over the phone.
por la que()
A phrase is a group of words commonly used together (e.g., once upon a time).
a. by which
La ruta por la que se administrará el medicamento depende de la droga en sí.The route by which the medication will be administered is dictated by the drug itself.
a. through which
Había sangre en la ventana por la que escaparon los ladrones.There was blood on the window through which the burglars escaped.
