单项选择题

It is implied in the passage that _____.

A．many industrialists feel no concern for the improvement of pollution control
B．breathing low concentrations of urban dust does not necessarily sicken or kill people
C．no acceptable biological mechanism has been suggested to explain the toxicity of low concentration of urban dust
D．scientists have done nothing to reveal the mystery of the toxicity of low concentration of urban dust

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单项选择题Which of the following statements about human alveolar macrophage is TRUE

A．Airborne dust may trigger suppressor macrophage suicides.
B．Airborne dust may trigger stimulatory macrophage suicides.
C．The ratio of suppressor macrophages to stimulatory ones in people with lung diseases is much higher than that in people with healthy lungs.
D．Only stimulatory macrophages show responses to airborne dust.

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

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.

单项选择题Why does the author introduce Abstract Expressionist painter

A．He wants to provide an example of artists who, like serious contemporary photographers, disavowed traditionally accepted aims of modem art.
B．Be wants to set forth an analogy between the Abstract Expressionist painters and classical Modernist painters.
C．He wants to provide a contrast to Pop artist and others.
D．He wants to provide an explanation of why serious photography, like other contemporary visual forms, is not an should not pretend to be an art.