How Do We Determine the Amount of Dark Matter in Elliptical

How do we determine the amount of dark matter in elliptical galaxies?

A) We measure the orbital velocities of star-forming gas clouds in the outer portion of the galaxy.
B) We measure the broadening of the galaxy's absorption lines to infer the speeds of stars at different distances from the galactic center.
C) We count the number of stars in the galaxy. Combining this with the galaxy's volume, we can calculate the galaxy's density.
D) We search for dark lanes of dust and black holes within the galaxy.
E) We measure how fast the galaxy rotates as a whole.