Who gave you permission to enter?

Let's analyze the options:
Option A: By whom were you given permission to enter?
This is the correct answer. The original sentence has "who" as the subject (the one performing the action of giving permission). In the passive voice, "you" becomes the subject (receiving the permission), and the verb changes to "were given." "By whom" indicates the agent (the person who gave permission). The word order correctly reflects passive voice structure.

Option B: By whom was you given permission to enter?
This option is incorrect because it uses the incorrect verb conjugation. "Was" should be "were" to agree with the plural pronoun "you".

Option C: By whom you were given permission to enter?
This option is grammatically incorrect. The word order is flawed. The passive construction requires the auxiliary verb ("were") to come before the subject ("you").

Option D: By whom were given you permission to enter?
This option is incorrect due to the incorrect word order. The auxiliary verb "were" and the past participle "given" should come before the subject "you".