At the US Supreme Court Level the "Rule of Four" Refers to Refers

At the U.S. Supreme Court level the "rule of four" refers to which of the following?

A) The requirement that four of the nine justices must agree to reverse a lower court's decision.
B) The fact that each justice is furnished four law clerks for assistance in research and writing.
C) The fact that four of the nine justices must agree to place a case on the Court's docket.
D) When a decision is rendered on a 5-4 vote of the nine justices, the fact that four justices have dissented conveys that the decision is not given great weight by lower tribunals.