为了得到函数的图象，可以把函数的图象适当平移，这个平移是（   ）

A：沿轴向右平移个单位

B：沿轴向右平移个单位

C：沿轴向左平移个单位

D：沿轴向左平移

    Today, astronauts wear very different protective clothing. It lets them move, do useful tasks, and stay outside their spacecraft in comfort and safety for several hours. The spacesuit is called the shuttle extravehicular mobility unit or EMU. It was designed to endure longer and to permit more movement than earlier spacesuits.

    The EMU has a number of parts that an astronaut can link together by using only one hand, which makes it possible for each astronaut to select the parts that fit correctly.

    Nowadays, NASA scientists are also considering the kind of spacesuits that would be needed for exploration on the planet Mars. Because of the gravity on Mars, spacesuits may have to be designed to be lighter than suits used in orbit or on the moon. The equipment may also have to protect astronauts from dust carried in the winds on Mars. And, they must be easy to repair and keep clean during a longer flight to and from the red planet.