What are large particles that are rolled or pushed on the bed of the stream called?

Which of the following terms describes the layers of air surrounding the earth ?

Dubai is challenged by all of the following environmental factors except a. a warm and dry climate b. a lack of annual rainfall c. scarce freshwater resources d. a lack of valuable natural resources

In 2002, north korea announced that it was shutting down its nuclear facilities constructing a hydroelectric energy plant restarting nuclear weapon development changing to a free market economy