HM Had Undergone Surgery That Resulted in His Memory Disorder

H.M. had undergone surgery that resulted in his memory disorder. Why did the surgeon need to perform such a radical surgery?

A) The surgery was necessary to stop his brain haemorrhaging caused by a collapse in the coal mine where he worked.
B) The surgery was a procedure done to relieve his severe epileptic seizures.
C) The surgery was an experimental procedure to treat his severe schizophrenia symptoms.
D) The surgery was the removal of a metastatic tumor in the left hemisphere of his brain.