Which of the following planets is most likely to be colder than Earth?
A) A planet with a thinner atmosphere, twice as far from the Sun, covered in ice
B) A planet with a thicker atmosphere, twice as far from the Sun, covered in forest
C) A planet with a thinner atmosphere, half as far from the Sun, covered in forest
D) A planet with a thicker atmosphere, half as far from the Sun, covered in ice