What Would Happen If the Andromeda Galaxy (A Spiral About

What would happen if the Andromeda Galaxy (a spiral about the same size as the Milky Way Galaxy) collided with the Milky Way?

A) The two galaxies would pass through each other, the stars sailing past one another unharmed, and the interstellar gas and dust clouds would collide to produce a burst of star formation.
B) The two galaxies would pass through each other almost unchanged with essentially no interactions at all.
C) The two galaxies would shatter or even explode, essentially destroying their stars and any life forms that there may have been (including us) .
D) All the gas and dust clouds and a great many of the stars would collide with each other, stopping both galaxies and creating a galactic merger.