Measurements of the orbital speeds of stars in the Milky Way and other galaxies have revealed that there must be a great deal of nonluminous mass in their outer reaches to make the rotational speeds remain high far away from the galactic centers. At distances of 15000 pc from the center of the Milky Way, the rotational speeds of stars is still 250 km/sec. What is the distance to the center

answer: 0.20

explanation: this can only be the answew because all the other measuremnets are not close

answer;

d. are made mostly of liquid

explanation;

-the general   composition and structure planets includes; they have a thick gas and liquid layer covering a small,solid core. mostly the gases are hydrogen and helium atmosphere and layers of liquid hydrogen. for instance neptune and uranus are examples of the outer planets, they have a core covered by ice and ammonia.

-neptune's atmosphere is hydrogen and helium with a bit of methane so there is no oxygen to breath and the interior is made up of frozen water and ammonia with a rock and iron core. thus, there is no liquid water or solid surface to survive.