Astronomers are interested in finding planets outside of the solar system, called exoplanets. There are two categories of exoplanets that are not found in the solar system. One of them is exoplanets with a radius of 1.9 - 3.1 Earth radii. What is the other category?
a) 0.5 - 0.7 Earth radii
b) 0.7 - 1.2 Earth radii
c) 5.1 - 8.3 earth radii
d) 1.2 - 1.9 Earth radii
e) 3.1 - 5.1 Earth radii