Which of the Following Methods Uses Astrometry to Detect Extrasolar

Which of the following methods uses astrometry to detect extrasolar planets around other star systems?

A) detection of Doppler shifts in the spectra of the parent stars
B) detection of reflected starlight
C) detection of brightness changes in a star as a planet passes in front of it
D) regular changes in the positions of the parent stars with respect to more distant stars as they move across the sky