__________ is/are evidence that spiral arms extend across the Milky Way disk.
A. Globular cluster positions.
B. Positions of massive main sequence stars.
C. The Doppler effect.
D. Radio waves from cold hydrogen gas clouds.
Answer:D
__________ is/are evidence that spiral arms extend across the Milky Way disk.
A. Globular cluster positions. B. Positions of massive main sequence stars. C. The Doppler effect. D. Radio waves from cold hydrogen gas clouds.