Which of the Following Describes the Way That Ring Galaxies

Which of the following describes the way that ring galaxies are believed to form?

A) when two spiral galaxies collide, along a direction parallel to one galaxy's disk
B) when two galaxies of different sizes collide along a direction perpendicular to the larger galaxy's disk
C) when two elliptical galaxies collide at a position offset from their centres
D) when more than two galaxies collide at the same time, along a straight line