题目内容：
The reason why the authors argue that the gun market may be threadbare partly because the drug market is so plump is_____
A．that the drug transaction is more profitable than gun-dealing B．that the police are more dedicated to the gun-dealing than to the drug-dealing
C．that the gang-leaders are suppressing the gun-dealing in order to maintain their profit from drug
D．that the gang-leaders are worried about the effect of crime on commerce
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