What Is the Cause of Millisecond Pulsars

What is the cause of millisecond pulsars?

A) As a pulsar cools, it collapses further. This causes its rotation rate to increase.
B) Pulsars in binary systems can draw mass from the binary companion. This mass, impacting the pulsar's surface, causes its rotation rate to increase.
C) The jets which radiate energy away from a pulsar cause it to become smaller and to rotate faster.
D) The rotation period for most pulsars is actually less than a millisecond. So the natural slowing as it loses energy moves it into the millisecond range.