How would you make this sentence impersonal in Spanish? "Someone has stolen my bag. "

Question

This is a great example of the stuff that really ticks me off with Progressive! In two consecutive tests, this answer has been given as "me ha robado el bolso" and "me han robado el bolso"    ----  WHICH IS IT?! The fact that one version of the indirect pronoun is obvious, but how is one supposed to know which one you are asking for?!!

Accepted Answer

Hola Diane,
The lesson is called "Impersonal sentences using the ellos form of the verb." Straight away this points you to plural conjugations [ellos = them]. The lesson states that there are different ways of doing impersonal sentences e.g. using the passive voice or the impersonal se, and gives the above construction [ellos = them = plural] as the subject of the lesson. In other words it ONLY uses the plural form.
So .... ha robado wouldn't be a plural construction becase "he" is singular for "he has or she has." Therefore the answer must be "han robado" ... plural ..... they have stolen. 
Saludos. John