题目内容：
根据材料，回答问题。C
Air pollution is caused by many things, Great clouds of smoke come from factories. Cars sendsmoke and fumes into the air. Burning waste fills the air with bits of dirt. Even burning leaves addsmoke tothe air. Sometimes, planes cannot find their landing spots through smoke. Smoke of allkinds" is bad to breathe and can do great harm to the body.
Still, we cannot live without air. We must find a way to clean the air we have,
In time, we may have factories that are run by atomic energy. Our cars may run on smoke-freeelectric power. Scientists are also working on new ways to help the oil burned by cars from makingfumes. Waste may be burned ,in the sand on ocean floors.
These changes might keep our air clean in the years to come. But until then, many scientistsare looking for ways to make air cleaner now.
On the whole, this passage is about A．dirty air
B．electric power
C．atomic energy
D．burning waste
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