Which best describes Mercury's plains?
a. heavily impacted with craters and large rays
b. solidified lava flows that are a uniform gray color
c. a geologically active surface of molten lava
d. solidified lava flows rich in dark basalts
e. a rich layer of soil containing iron and silicate
Question 2
A planetary nebula is a(n) ____.
a. expanding envelope of ionized gas expelled by a dying medium-mass star
b. expanding envelope of neutral gas and dust expelled by a dying medium-mass star
c. contracting envelope of dusty material from planets destroyed by a dying medium-mass star
d. contracting envelope of ionized interstellar medium absorbed by a dying medium-mass star
e. expanding atmosphere of a medium-mass star as it becomes a red giant
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