What type of reflecting surface is useful for hearing an echo?

A. दूर और hard surface / Distant and hard surface

Step 1: Identify the concept: this is sound reflection. Step 2: A hard and distant surface can reflect sound with enough time gap so echo is heard. Step 3: Remember echo needs a hard distant reflector.

Step 1: concept पहचानें: यह sound reflection है। Step 2: Hard और distant surface sound को reflect करके enough time gap दे सकती है जिससे echo सुनाई देती है। Step 3: Echo needs hard distant reflector याद रखें।