Which of the following would be the most difficult consumer characteristic for firms to use in price discrimination?

Suppose that there are two goods, X and Y, that are competing for dominance in a market with network externalities.  Furthermore, suppose that the market has chosen good X even though it is inferior to good Y and that the net benefits of switching from X to Y are $20 while the costs of switching are $30.  If the market stays with good X, then __________________ has occurred.  If the costs of switching were to fall to $15 and the market still stays with good X then ___________________________.

A. no market failure; market failure has occurred. B. market failure; no market failure has occurred. C. no market failure; there will still be no market failure. D. market failure; there will still be market failure.

If the income-consumption path slopes upward, then:

A. both goods are normal goods. B. both goods are inferior goods. C. the goods are substitutes. D. the goods are complements.