How does the text describe Pluto? 
 a
 Pluto is made up entirely of ice, and it is bigger than Venus.
 b
 Pluto is made up entirely of rock and ice, and it is bigger than Earth's moon.
 c
 Pluto is made up entirely of gas, and it is bigger than Earth's moon.
 d
 Pluto is made up entirely of rock and ice, and it is smaller than Earth's moon.