Which of the Following Represent(s) the Standard Established by the Court

Which of the following represent(s) the standard established by the Court in United States v. Ramirez for determining whether the police do not have to knock and announce before executing a search warrant?

A) The reasonableness of the police action is based on a determination that the facts and circumstances of the particular entry justified entry without a knock and announce.
B) The police must have reasonable suspicion that the knock and announce would serve no purpose.
C) The police must have reasonable suspicion that the knock and announce would inhibit the effective investigation of a crime by allowing for the destruction of evidence.
D) Only a and c
E) All of the above