What is the BEST way to combine sentences 6 and 7?

a
Federal troops enforced the Fourteenth Amendment and guaranteed equal rights to all citizens.
b
Federal troops enforced the Fourteenth Amendment, this guarantees equal rights to all citizens.
c
Federal troops enforced the Fourteenth Amendment, which guarantees equal rights to all citizens.
d
Federal troops, the ones who enforced the fourteenth Amendment, guaranteed equal rights to all citizens.
What is the BEST way to combine sentences 6 and 7?

a
Federal troops enforced the Fourteenth Amendment and guaranteed equal rights to all citizens.
b
Federal troops enforced the Fourteenth Amendment, this guarantees equal rights to all citizens.
c
Federal troops enforced the Fourteenth Amendment, which guarantees equal rights to all citizens.
d
Federal troops, the ones who enforced the fourteenth Amendment, guaranteed equal rights to all citizens.