The Marginal Rate of Substitution of Beef for Chicken Is

The marginal rate of substitution of beef for chicken is the

A) number of units of chicken the consumer is prepared to give up to obtain one more unit of beef.
B) number of units of beef the consumer is prepared to give up as income falls.
C) number of units of beef the consumer must sacrifice to obtain one more unit of chicken.
D) rate at which units of beef may be exchanged for units of chicken in the market.