What Observations About Disks of Dusty Material Around Young Stars

What observations about disks of dusty material around young stars suggest that planets may be forming in such disks?

A) the disks give off x-rays and gamma-rays characteristic of small planets
B) the disks show lanes that are empty of dust within them
C) the disks show evidence of very strong winds coming from the star
D) the disks are making the stars "wiggle" -- move back and forth across the sky -- in a way that can be observed even with small telescopes
E) radio telescopes have revealed transmissions from the disks that include rap songs and other evidence of advanced civilizations
Section 21.4: Planets Beyond the Solar System: Search and Discovery