单项选择题

The danger is that natural processes are being so fundamentally altered by human activities that once ______ these changes cannot be switched off.

A. begins
B. having begun
C. beginning
D. begun
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单项选择题
It has created a world of mobility: of rapid and ______ change, with attention focused mainly on novelty or utility.
A. increasing
B. constant
C. lengthy
D. consistent
单项选择题
Much time was spent in these groups, adopting problem-solving ______ to specific cases from the participants.
A. means
B. approaches
C. methods
D. ways
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