What Would Happen If the Andromeda Galaxy (A Spiral About

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

A) The two galaxies would pass through each other,the stars sailing past one another unharmed,while the interstellar gas and dust clouds would collide and stop,thereby becoming extremely heated.
B) The two galaxies would pass through each other almost unchanged,with essentially no interactions at all.
C) The supermassive black holes of the two galaxies would collide and explode,the resulting radiation essentially destroying their stars,planets,and any life forms that there may have been (including us) .
D) All of 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.