Answer to Question 1
The geothermal gradient is an increase in temperature with depth, which varies from place to place, averaging about 25C per kilometer in the upper crust. A typical geothermal gradient is compared to the melting point curve for the mantle rock peridotite; the temperature at which peridotite melts is higher than the geothermal gradient. Thus, under normal conditions, the mantle is solid.
Answer to Question 2
C