What Two Observations Allow Us to Calculate Mass of the Portion

Multiple Choice

What two observations allow us to calculate mass of the portion of the Galaxy within the Sun's orbit?

A) the Sun's mass and its age
B) the Sun's composition and luminosity
C) the Sun's age and period of the Galactic Year
D) the Sun's orbital velocity and its distance from the Galactic Center
E) the Sun's mass and velocity in orbit of the Galactic Center