Earth Science i really need help with
18. The apparent backward movement of a planet is called
A. heliocentric motion.
B. retrograde motion.
C. eccentricity.
D. Kepler's first law of motion.
19. Who first introduced the idea that the Sun is the center of the universe?
A. Nicolaus Copernicus
B. Johannes Kepler
C. Albert Einstein
D. Edwin Hubble
20. The four giant gas planets that are made primarily of lightweight elements are
A. Venus, Saturn, Uranus, and Neptune.
B. Jupiter, Saturn, Uranus, and Neptune.
C. Earth, Saturn, Neptune, and Venus.
D. Mercury, Venus, Earth, and Neptune.