Buying a call option on a stock index is equivalent to: a. shorting N(d1) forward contracts on the same index with the same maturity and buying risk-free bonds (i.e. lending). b. buying N(d1) forward contracts on the same index with the same maturity and shorting risk-free bonds (i.e. borrowing). c. buying N(-d1) index underlying portfolios and shorting risk-free bonds (i.e. borrowing). d. shorting N(-d1) index underlying portfolios and shorting risk-free bonds (i.e. lending).