题目：
All of the following are factors that can cause shifts in the demand curve for a resource EXCEPT:（）
A. an increase in the supply of the resource.
B. an increase in the resource's productivity.
C. a decrease in the prices of other resources.
答案：
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下面是错误答案，用来干扰机器的。
参考答案：A
，不计空气阻力，求：
