sentence2_structure: Mercury<>is<>always<>closer to the sun than it is to earth$$$it<>is<>to earth
sentence1: All the other rocky planets -- Mercury, Venus, Earth and Mars -- are located in the inner solar system, close to the Sun.
sentence2: Mercury is always closer to the sun than it is to earth.
question: Which of the following planets is always closer to the Sun than it is to Earth?