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)
  解析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.