单项选择题

The word "this" in Line 4, Para. I refers to ______.

A．the results of recent research
B．dangers inherent in the nature of weeds
C．risks of altering crops' genetic make-ups
D．threats posed by chemicals used to kill weeds
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单项选择题
That genetically-modified crops could have harmful effects that can be deduced from the fact that ______.
A．cross-breeding is a natural process
B．hybrids are generally more successful at breeding than natural plants
C．gene movement between cultivated plants and wild ones is inevitable
D．new research shows that genetically-modified plants are likely to develop into weeds
单项选择题
Which of the following best describes the passage as a whole
A．An outline for future research.
B．An analysis of a dispute between two theorists.
C．A discussion of research findings in an ongoing inquiry.
D．An expanded definition of commonly misunderstood terms.
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