What are the spiral arms of the milky way made of?

a. older stars and comets
b. variable stars
c. asteroids and comets
d. younger stars and gaseous nebulae

the spiral arms of the milky way was made of: D. younger stars and gaseous nebulae The spiral arms of the mily way was organized into four spiral arms, and since it was made of younger stars and gaseous nebulae, Spiral arms typically contain a higher density of interstellar gas and dust than the Galactic average as well as a greater concentration of star formation

Ithink i might know wait one second let me serve

The reason why i feel that the theory of plate tectonics is correct because scientists have found dinosaur bones of the same species in africa, asia, and in the americas. which means that they must have been together at one point in time. plate tectonics is also how the hawaiian islands were formed. as the plate hawaii is on was moving north west, magma would melt through the sea bottom and hardening. forming into the island chain. plate tectonics also explains the mariana trench. two plates were moving away from each other and made a giant crack in the ocean floor running 2,550 kilometers (1,500 miles)  long.