What's the name for the part of earth made of rock apex?

In the diagram below dab and dac are adjacent angles

[ou.01jthe greatest speed with which any physical object moves is 300,000 km/soundsec. which of the following has a speed of 300,000 km/sec? a. light in water b. light in vacuum c. sound in air. d. sound in water

Witch of the following volcano hazards is made up of rocky particles about the size of a grain of sand