Once, William, Mike, Mary and Lisa went out for a travel by plane. On the way back home, the plane was out of gas and there were only three parachutes for emergency. Therefore one guy had to jump without wearing parachutes. Since William was the oldest guy, he had the right to decide everything. ¡§Now I have to ask each of you a question. If you can answer it, then you will get a parachute¡¨, said William. ¡§How many suns are there in the sky?¡¨ he asked Mike. ¡§One¡¨ Mike jumped with his parachute. ¡§How many moons are there in the sky?¡¨ he turned to Mary. ¡§One¡¨ Mary jumped with her parachute. ¡§How many stars are there in the sky?¡¨ he asked Lisa. Astonished and sadly, Lisa jumped out of the plane. Luckily, she landed in a lake and was safe. A few months later, they were out in a plane for fun again. The same tragedy took place again. Only three parachutes for emergency again. This time William asked each of them a question again to decide who will jump without a parachute. ¡§Tell me the capital of USA.¡¨ ¡§Washington D.C.¡¨ Mike was lucky to get one and jumped out of the door. ¡§How many states are there in USA?¡¨ ¡§Fifty states¡¨ So did Mary. ¡§How many planets are there in the galaxy¡¨ William turned to Lisa. Lisa, poor thing, had to jump with a parachute again. Luckily, she landed safely into a pool. Another few months later, these four went out again by plane. The plane didn¡¦t work on the way to an island. This time even before William asked questions, Lisa jumped out of the door after hearing the bad news. ¡§Lisa, wait. We¡¦ve got four parachutes!¡¨ shouted William.