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