Who Is Most Likely Suffering from Retrograde Amnesia

Who is most likely suffering from retrograde amnesia?

A) Billy,who can't seem to learn a foreign language
B) Mariana,who struggles to remember the names of the people she just met
C) Cecil,who can't remember much of anything after his wife died
D) Margie,who can't remember much of anything prior to being attacked on the street after a late-night party