An echo is heard when sound is reflected off a surface. Which of the following best explains this phenomenon?

A. Sound waves strike a barrier and then spread out radially toward an observer.

B. Sound waves travel from one medium to another, bend, and travel back toward an observer.

C. Sound waves bounce off a barrier and then travel back toward an observer.

D. Sound waves are absorbed and reemitted by a barrier. Then, the waves travel back to an observer.