Which of These Methods Has Provided Strong Evidence for the Existence

Multiple Choice

Which of these methods has provided strong evidence for the existence of hundreds of planetary systems around other stars?

A) detection of very regular pulses of radio energy from some stars.
B) spectroscopic evidence of large quantities of molecules such as ammonia and methane, which can exist only in planetary atmospheres.
C) direct photography of actual planets near other stars.
D) periodic wobbling of the positions and spectral line displacements of several nearby stars.