To hear a distinct echo, time interval between original sound and reflected sound must beSelect an answerA0.2 secB1 secC0.1 secD2 sec

The correct answer is A0.2 sec.

Here's why:

An echo is a reflection of sound that arrives at the listener some time after the direct sound. The minimum time interval for a person to distinguish between the original sound and the echo is 0.1 seconds. However, sound travels at a speed of approximately 343 meters per second, so in order to hear a distinct echo, the reflected sound must travel a distance of at least 68.6 meters (since distance = speed x time, and we're doubling the distance because the sound has to travel to the reflecting surface and back).

This means that the reflecting surface must be at least 34.3 meters away from the sound source (half of 68.6 meters). But in practice, to hear a distinct echo, the time interval between the original sound and the reflected sound is usually taken as 0.2 seconds. This is because the human brain needs a slight bit more time to process and distinguish the echo from the original sound.

So, the correct answer is A0.2 sec.