Is the pronoun referring to a person?
No
Yes
Is it after a perposition like the personal a?
Yes
No
Is it singular or plural?
Singular
Quien
Plural
Quienes
Is it at the begining of the sentence?
Yes
No
Lo que
Is it an abstract idea?
Yes
Lo que
No
que
Is it within commas?
Yes
Singular or plural?
Singular = quien
Plural = quienes
No
Que