Read these sentences from the text. "Freed and his colleagues studied the New Madrid faults for 10 years.

"They expected to see the ground slowly twisting and turning, causing stress to build up in the rocks."

Why did Freed and his colleagues expect to see the ground slowly twisting and turning?

because tectonic plates fit together like pieces in a jigsaw puzzle
because most earthquakes happen at the boundaries of tectonic plates
because California lies atop a boundary where the Pacific Plate meets the North American Plate
because the movement of the ground on either side of a fault is usually what causes stress to build up in rock