—It can't work.

They will also need air people there can breathe.

There hotels on the Moon .

    The rockets take astronauts (宇航员) and man-made satellites (卫星) into space. The satellites are used for communication (通信), weather monitoring and research. But how do satellites stay up without falling down?

    There are two opposite forces (力量) acting on the satellites. One of them is the force of gravitation (地心引力), which tries to pull the satellites towards the Earth. The other force is created by the rotation (旋转) of the satellite around the earth. This force tries to take the satellite away from the Earth. With these two forces, the satellite goes round and round. The gravitational pull of the Earth (the force which pulls everything towards the ground) is like a rope which keeps the satellite from flying away.

    Everything that goes up has to come down. It is only a matter of time before a satellite comes back to the Earth. As time goes by, the satellite loses its speed, which makes the gravitational pull stronger than the force pulling it away. This makes the satellite crash down (坠落) to the Earth.

—Let's ________ a party to welcome him.

Allen's younger brother is when his mum .