阅读理解
Uncle Li and Uncle Wang are good friends. They live next to each other and their farms are both at the foot of the mountain. So they can help each other. But neither of them likes to use his head. They're both poor though they work hard. Most villagers have built new houses, but they still live in the low and broken houses. They never find out why. Once Uncle Li went to town to buy some medicine for his wife. In the town he heard the apples in a city were expensive. He told Uncle Wang about it as soon as he went back. They decided to carry some apples to the city. They borrowed some money from their friends and bought nearly 1,000 kilograms of apples in the villages and carried them to the city on a tractor. Bad luck! A lot of apples has already been carried there when they arrived A few days later they had to sell them at a low price 。They felt unhappy and returned to their village. "I can't understand why we sustained 蒙受) losses in business while others always profit "Uncle Li asked one day.
"The tractor was too small "Uncle Wang said without thinking. "We'll carry more apples on a truck next time!"
"I agree!" said Uncle Li. "How foolish we were!"
到达“48小时轨道”和“72小时轨道”，最后奔向月球。如果按圆形轨道计算，并忽略卫星质量的变化，则在每次变轨完成后与变轨前相比
