The shuttle flies to the earth at ______ an hour after reentering the atmosphere.

A．They spend most of their time looking through telescopes.
B．They are constantly analyzing data.
C．They often live near observatories.
D．They devote a lot of time to theoretical problems.

A．To decrease the time it takes to photograph objects.
B．To avoid using a telescope.
C．To sharpen the color of what they observe.
D．To obtain images of distant objects.