What Has Been a Major Problem in Interpreting the M'Naghten

What has been a major problem in interpreting the M'Naghten rule?

A) To be accurate in deciding when a defendant is unable to assist in his or her own defense
B) To be accurate in deciding where to hold the accused before trial
C) To define precisely what the term insanity means
D) To define clearly and consistently which disorders constitute diseases of the mind