An investor who owns a S&P 500 index ETF (a fund that tracks the value of the stocks in the S&P 500 index) can fully hedge against a decline in the market by:

a. Writing a covered call (selling a call option on the S&P500 ETF).

b. Writing a naked call of the S&P 500.

c. Selling a put option on the S&P 500.

d. Buying a put option on the S&P 500