Which of the measurements does not help to deduce the m of the black hole at the center of our Galaxy?

C. The spectral types would be insufficient proof of a black hole's m. The m however would warp space-time and cause disruptions in the stars nearby orbits, velocity, and the warp would bend the light of the star such as the 1919 solar eclipse showed the sun's warp bent light from stars and changed their apparent position. The period of the star's orbit shows how fast they orbit, surely the m and warp again would affect this.