Whispering galleries are remarkable acoustic spaces found beneath certain domes or curved ceilings. A famous one is located outside a well-known restaurant in New York City’s Grand Central Station. ( ① ) It’s a fun place to take a date: the two of you can exchange romantic words while you’re forty feet apart and separated by a busy passageway. ( ② ) You’ll hear each other clearly, but the passersby won’t hear a word you’re saying. ( ③ ) To produce this effect, the two of you should stand at diagonally opposite corners of the space, facing the wall. ( ④ ) Ordinarily, the sound waves you produce travel in all directions and bounce off the walls at different times and places, scrambling them so much that they are inaudible when they arrive at the ear of a listener forty feet away. ( ⑤ ) But when you whisper at a focus, the reflected waves all arrive at the same time at the other focus, thus reinforcing one another and allowing your words to be heard.[3점]

* acoustic: 음향의 ** diagonally: 대각선으로