单项选择题

This passage is mainly about _____.

A．how inhaled dust harms the lungs
B．the function of Environmental Protection Agency
C．the function of human alveolar macrophages
D．studies by Environmental Protection Agency

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单项选择题

According to this passage, Environmental Protection Agency _____.

A．is the only agency studying the effects of air pollution on health
B．has launched a surprised attack on researchers
C．has decided to decrease the permitted concentration of airborne dust
D．has tremendously improved pollution control

单项选择题

How did the nineteenth-century defenders of photography stress the photography

A．They stressed photography was a means of making people happy.
B．It was art for recording the world.
C．It was a device for observing the world impartially.
D．It was an art comparable to painting.