What are the three main parts of our galaxy? Describe them.
a) Core, halo, spiral arms; Core contains old stars, halo contains gas and dust, spiral arms contain young stars
b) Core, spiral arms, halo; Core contains young stars, spiral arms contain old stars, halo contains gas and dust
c) Core, halo, spiral arms; Core contains gas and dust, halo contains old stars, spiral arms contain young stars
d) Spiral arms, core, halo; Spiral arms contain gas and dust, core contains old stars, halo contains young stars