What Causes a Meteor Shower

What causes a meteor shower?

A) If Earth happens to be near a comet when it breaks up, we will see a shower as debris enters Earth''s atmosphere.
B) Earth passes through the orbit of a comet. If the comet happens to be nearby, the normal ejecta from the nucleus will cause a shower.
C) Earth passes through the tail of a comet.
D) Earth passes through the orbit of a former comet that has become strewn with debris. This enters our atmosphere and causes showers.