During a supernova, the outer layers of a star are blown off and the star's core shrinks down by a factor of 10,000 or more to form a neutron star. As the core shrinks, conservation of angular momentum says that

a. the core will spin faster.
b. the spin of the core does not change.
c. the core's rotational axis will precess rapidly, forming a pulsar.
d. the core will spin more slowly.