Спільний звук

What has keys but can’t open locks? ... The answer is: Keyboard. --- I speak without a mouth and hear without ears. What am I? ... The answer is: Echo. --- The more you take, the more you leave behind. What are they? ... The answer is: Footsteps. --- I have cities, but no houses; forests, but no trees. What am I? ... The answer is: Map. --- What com