The echo (reflected sounD. will be distinctly heard only at ordinary temperatures if the distance of the reflecting surfaces from the source of sound is at least ________?

(A) 1120 ft (X)
(B) 120 ft (X)
(C) 56 ft ()
(D) 100 ft (X)
(E) None of these (X)

Answers: The echo (reflected sounD. will be distinctly heard only at ordinary temperatures if the distance of the reflecting surfaces from the source of sound is at least 56 ft.