According to a survey of graduating medical students conducted by the Association of American Medical Colleges, minority graduates are nearly four times more likely than are other graduates in planning to practice in socioeconomically deprived areas.
(B) minority graduates are nearly four times more likely than other graduates who plan on practicing
(C) minority graduates are nearly four times as likely as other graduates to plan on practicing
B: more likely than .....to do what?! The abrupt "who" interrupts the flow of meaning.
We need to keep the idiom "likely to ....."
--> eliminate B.