英语缺词填空Since t---------- of millions of years the moon has be

英语缺词填空Since t__________ of millions of years the moon has been going round the earth.A_____
Since t__________ of millions of years the moon has been going round the earth.A_____ this time.The moon was the only satellite(卫星)of the e_______.Today the earth has many other satellites.All of them are made by man.These man-made satellites are m_______ smaller than the moon.Some of them will still go round the earth thousands of years.
Man-made satellites don’t f_____ because they are going too fast to do s_____.The pull of the earth k______ them from doing this.As a result,they travel in an orbit(轨道)round the earth.
If a man-made satellite travels about a certain height,it can keep g_________ round the atmosphere(大气),and there is n________ to slow it down.If it travels lower than that,it will be slowed down so m_____ that it will fall to the earth.