The Presence of a Very Large Amount of Unseen Matter

The presence of a very large amount of unseen matter ("dark matter") in the halo of the Milky Way Galaxy is deduced from

A) the rotation curve of the Galaxy, in which orbital speeds of stars appear to obey Kepler's law.
B) the rotation curve of the Galaxy, in which orbital speeds of stars in the outer regions of the Galaxy are significantly higher than is predicted by Kepler's law in which the value for the observed mass in the Galaxy is used.
C) the unexpected absence of luminous matter (stars, and so on) beyond a certain distance from the galactic center.
D) the high amount of interstellar absorption in certain directions.