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 ________...? Mcqs

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

(B) 120 ft

(C) 56 ft

(D) 100 ft