单项选择题

The potential for hazardous weeds developing from genetically-modified plants is greatest for ______.

A．agricultural crops grown for their content
B．crops' that are closely related to their weeds
C．areas in which cross-breeding is kept to a minimum
D．crops who rely on herbicides and pesticides for effective harvests
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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
单项选择题
The author suggests that the main impact that gene transfer between crops and weeds could have is ______.
A．the collapse of the agricultural industry
B．the rapid development of unintended plant hybrids
C．the development of pest and herbicide-resistant weeds
D．the difficulty to determine whether to make crops resistant to pests or not given the limited nature of current research
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