Which of the following statements best explains why supply tends to be more price elastic in the long run than in the short run?

a.

Supply curves are steeper over long periods of time than over short periods of time.

b.

Buyers of goods tend to be more responsive to price changes over long periods of time than over short periods of time.

c.

The number of firms in a market tends to be more variable over long periods of time than over short periods of time.

d.

Firms prefer to change their prices in the short run rather than in the long run.

If isoquants are L-shaped, it means that the two inputs are:

a.

perfect substitutes

b.

perfect complements

c.

partial substitutes

d.

none of the above