What does Earth's crust and uppermost mantle form?

A. asthenosphere

B. hydrosphere

C. lithosphere

D. atmosphere

Earth's inner core is solid because of

A. the composition of its rock.

B. its great diameter.

C. extreme cold.

D. immense pressure.

The answer to the first question is (C). The lithosphere includes the crust and the cooler upper part of the upper mantle. It averages about 50 miles in thickness, give or take ten miles.

The answer to the second question is (D), the innder core is solid because of immense pressure.