What Does the "Rule of Sixty" in the Senate Mean

What does the "rule of sixty" in the Senate mean?

A) A bill needs sixty positive votes to be able to move to the floor of the Senate
B) Sixty senators need to be present in order for a bill to move to the floor of the Senate
C) Sixty votes are needed to overturn a presidential veto
D) If sixty senators vote against a bill, then they cannot use the reconciliation process