How the earth's crust is distinguished from the earth's mantle?

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.

Which barrier to economic development is shown in the following examples?

Which of the following types of tourist are best to bring money to the local southeast asian communities