Solid rock is much denser than liquid magma when the relatively cool rock of a tectonic plate enters the liquid lower mantle how would you expect the cool rock to move within the liquid portion of the mantle ?

Which of the following is not a challenge to instituting sound global environmental policies? a. most changes are inexpensive and easy to implement. b. elected leaders who support unpopular environmental issues often are not re-elected. c. economic considerations outweigh environmental ones in many societies. d. there is no way to enforce international environmental agreements.