Spiral Galaxy Rotation Curves Are Generally Fairly Flat Out to Large

Multiple Choice

Spiral galaxy rotation curves are generally fairly flat out to large distances.Suppose that spiral galaxies did not contain dark matter.How would their rotation curves be different?

A) The orbital speeds would fall off sharply with increasing distance from the galactic center.
B) The orbital speeds would rise upward with increasing distance from the galactic center,rather than remaining approximately constant.
C) The rotation curve would be a straight,upward sloping diagonal line,like the rotation curve of a merry-go-round.
D) The rotation curve would look the same with or without the presence of dark matter.