When two plates of continental lithosphere collide

a. the plates become sutured together and mountains form

b. a rift valley forms

c. has a granitic composition

d. is thicker than continental lithosphere

When two plates collide, mountains start forming. The plates push on each other, "curving" the edges. The taller the mountain, the longer the plates have been colliding.

heat from the core of the earth causes convection currents to occur in the mantle. these currents slowly move the crust around.