Tycho Brahe's contribution to Kepler's Laws of Planetary Motion werea. his detailed and accurate observations of the planet's position. b. his observations of Jupiter's moons. c. a mathematical explanation of epicycles. d. a precise lunar calendar. the correct explanation of lunar phases.

Which statement is the best definition of an atom? a) anything that has mass and occupies space. b) the smallest particle that has the properties of an element. c) a substance that cannot be broken down chemically into simpler substances. eliminate d) the smallest unit of a substance that exhibits all of the properties characteristic of that substance.