Measurements from Distant Galaxies Indicate That Supernovae Should Occur at a Rate

Measurements from distant galaxies indicate that supernovae should occur at a rate of two per century in a spiral galaxy such as the Milky Way, but only three have been recorded in our galaxy in the past 1000 years. Why is this?

A) Most supernovae produce x rays and radio waves but not visible light, and hence were invisible to earlier observers.
B) The majority of supernovae must have occurred in the plane of the Milky Way, and hence were hidden from Earth by the dense gas and dust in the Milky Way plane.
C) Observers were not watching the sky carefully enough, particularly through the Dark Ages and over the past few centuries.
D) The Milky Way Galaxy is somehow different, with much lower numbers of very massive stars in general, so many fewer stars have undergone supernova explosions.