Final answer:
Kepler's first law states that the orbit of a planet is an ellipse with its star at one focus, making the correct answer to the student's question 1) its star.
Step-by-step explanation:
According to Kepler's first law, the orbit of a planet is an ellipse with the star that the planet orbits at or near one focus. Therefore, the correct answer to the question is 1) its star. This elliptical orbit means that planets are sometimes closer to their star (at perihelion) and sometimes further away (at aphelion).