How Can Astronomers BEST Observe the 5-Minute Oscillations of the Sun's

How can astronomers BEST observe the 5-minute oscillations of the Sun's surface?

A) Zeeman-effect measurements of magnetically sensitive lines
B) high-resolution positional observations of the edge of the solar disk
C) measurement of the modulation of radio emissions from the solar surface, similar to the modulation used to transmit sound signals by radio on Earth
D) high-precision Doppler shifts of spectral lines