The lack of plate tectonics on other planets in our solar system likely means which of the following must be true? a. No other planet has a solid crust over a moving upper mantle. b. Earth has more layers than any other planet. c. Earth is the only planet with a magnetic field. d. No other planet has a warm interior.

If we represent the solar system on a scale that allows us to walk from the sun to pluto in a few minutes, then a) the planets are microscopic and the stars are millions of miles away. b) the planets are the size of basketballs and the nearest stars are a few miles away. c) the planets are marble size or smaller and the nearest stars are thousands of miles away.