Kepler modified Copernicus's model of the universe by proposing that the

Answer: Paths of the planets follow an elliptical orbit around the sun

Explanation:

Copernicus's model of the universe (heliocentric theory) was refuting the long life geocentric theory (the Earth as the center of the universe) proposed by Ptolemy and accepted by the Catholic Church.

However, the heliocentric theory did not explain why planets orbit the Sun at different speeds at different times, because this model used only circular orbits.

Years later, the astronomer Johannes Kepler refined the Copernicus' heliocentric theory with the introduction of elliptical orbits with the formulation of his three laws of planetary motion.

Where Kepler's 1st Law is a clear example:

The orbit of a planet around the Sun, is in the form of an ellipse with the Sun at one of the two foci of that ellipse.

Kepler modified Copernicus's model of Universe by proposing the theory that the orbit of the planet around the sun is in elliptical path taken by the planets to revolve around the Sun.

Explanation:

The path of the planetary motion was described by Kepler in order of modification of the model given by Copernicus.

Copernicus gave the model of planetary motion describing that the planets revolves around Sun which remains in center for all the planets. The path taken to revolve around Sun was not perfectly defined.