【单选题】A recent article suggests that the introduction of the new iPhone 5 increased the demand for iPhone protective cases. The article suggests that these two goods are
A.
substitutes and their indifference curves are close to being straight lines.
B.
complements and their indifference curves are close to being straight lines.
C.
substitutes and their indifference curves are close to being L shaped.
D.
complements and their indifference curves are close to being L shaped.