Suppose that the domestic risk free rate is r and dividend yield on an index is q. How should the put-call parity formula for options on a non-dividend-paying stock be changed to provide a put-call parity formula for options on a stock index? Assume the options last T years.

a. The stock price is replaced by the value of the index multiplied by exponent qT.

b. The stock price is replaced by the value of the index multiplied by exponent rT.

c. The stock price is replaced by the value of the index multiplied by exponent -qT.

d. The stock price is replaced by the value of the index multiplied by exponent rT.