Concept:An echo involves sound travelling to the cliff and returning to the observer, so the total distance is twice the observer–cliff distance.Explanation:Time taken for the sound to go and return is t=1.26s.Speed of sound is v=330ms−1.Total distance travelled by sound is vt=330×1.26.Distance of the observer from the cliff is half of this total distance:d=2vt=2330×1.26d=2415.8=207.9mAnswer:207.9m — Option B.