35. It was so a difficult mathematic puzzle that we could not do it.
IV. READING COMPREHENSION
A. Read the passage carefully and choose the correct answer.
Pollution can take two major forms: local pollution and global pollution. In the past, only local
pollution was thought to be a problem. For example, coal burning produces smoke, which in
sufficient concentrations can be a health hazard. One slogan, taught in schools, was "The solution
to pollution is dilution." The theory was that sufficiently diluted pollution could cause no damage. In
recent decades, awareness has been rising that some forms of pollution pose a global problem.
Human activity, primarily nuclear testing, has significantly raised the levels of background radiation,
which leads to human health problems, all over the 'world. Awareness of both 'kinds of pollution,
among other things, has led to the environmental movement, which seeks to limit the human
impact on the environment
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