How do we know that some layers of the earth are solid and some liquid?

What did the pattern of earthquakes in the wadati-benioff seafloor zones show scientists? a.) earthquakes occur where the ocean floor reaches its highest temperatures. b.) many earthquakes take place 700 kilometers below the seafloor. c.) slabs of ocean floor return to the mantle in subduction zones. d.) ocean - trenches cause earthquakes.

Because its government strictly controls its economy, north korea has a economy. a. command b. mixed c. traditional d. free market

In a class of 20 students, what democratic form of governance makes the most sense