Question：The supply curve for sofas has moved to the right. Which of the following could have caused this shift?
 
　　A. A decrease in the cost of horsehair (a raw material used in making sofas)
 
　　B. A decrease in the price of futons (a substitute)
 
　　C. A decrease in the price of sofas
 
　　D. A decrease in the wage rate in the futon industry
 
　　The correct answer is: A decrease in the cost of horsehair (a raw material used in making sofas)
 
　　As costs incurred in a producing sofas have fallen, producers will be prepared to produce more at any given price. A change in the price of sofas will lead to a movement along the supply curve. A decrease in the price of a substitute will lead to a decrease in the demand for sofas.

 
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