Strong Evidence for the Existence of Planetary Systems in the Process

Multiple Choice

Strong evidence for the existence of planetary systems in the process of formation around other stars comes from

A) spectroscopic evidence of large quantities of molecules such as ammonia and methane, which can exist only in planetary atmospheres.
B) images and infrared observations of disks of dust.
C) detection of very regular pulses of radio energy from some stars.
D) direct photography of actual planets near other stars.