On pain of death

 The Forbidden City in Beijing, from which the emperors ruled by heavenly mandate, was a site which a commoner or foreigner could not enter without any permission, on pain of death.
(A) which a commoner or foreigner could not enter without any permission,
(B) which a commoner or foreigner could enter without any permission only
(C) which no commoner or foreigner could enter without permission,
(D) which, without permission, neither commoner or foreigner could only enter,
(E) which, to enter without permission, neither commoner or foreigner could do,

 
To me C made most sense. But it seems C distorts the meaning of the sentence. Hence B is the best alternative.

The Forbidden City in Beijing, from which the emperors ruled by heavenly mandate, was a site which a commoner or foreigner could enter without any permission only on pain of death.
This says that the commoner or foreigner could enter, but they would die for for their actions.
C then that the commoner and foreigner cant enter, but then leaves on pain of death hanging and not refering to anything.