The right option is; C
All the inner planets are smaller than the outer planets is the statement that describes the size of the inner planets.
The inner planets include Mercury, Venus, Earth and Mars. They are also called terrestrial planets because they have solid rocky surfaces. All the inner planets are much smaller (diminutive) than the outer planets and they are closer to the Sun. Of all the four inner planets, Earth is the largest, while mercury is the smallest. The inner planets have either few moons or no moons and they are chiefly composed of heavy metals such as iron and nickel.