市场上某种产品存在超额需求是由于（）。
A.产品价格高于均衡价格
B.产品是优质品
C.产品供不应求
D.产品价格低于均衡价格
参考答案：D
Tom , you ____ play with the knife. You_____ hurt you. [ ]
A. won't; can't
B. mustn't ; may
C. shouldn't ; must
D. can't ; shouldn't
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