Option A - correct
The sentence correctly uses 'whom' which is an objective pronoun to show the receiver of the action.
Option B - incorrect
It uses the wrong form of pronoun 'whoever' to describe the object of the sentence.
Option C - incorrect
'Being' as used in the sentence gives it an ambiguous feeling which changes the intended meaning of the sentence.
Option D - incorrect
The addition of 'as' in this sentence makes it seem incorrect. If we omit the word 'as' and read the sentence as it was. It sounds really illogical.
Option E - incorrect
This has the same issue as option B. Also, 'who' is a subjective pronoun, it can't be used as an object.