A collar strategy provides protection against declines in the price of the underlying asset. By purchasing a put option, the investor has a right to sell the asset at a pre-determined price, offering protection against price declines. Writing a call option provides premium income and caps the potential profit if the asset's price rises significantly. This strategy provides both downside protection and potential for some upside gain.

A is incorrect. Writing a naked call option exposes the writer to potentially unlimited losses if the underlying asset's price rises significantly. However, the writer benefits if the price remains stable or declines, as they can keep the option premium.

C is incorrect. Purchasing a futures contract exposes the holder to potential losses if the price of the underlying asset declines. The holder benefits if the price increases.

D is incorrect. Writing a covered call option means holding the underlying asset and writing a call option on it. If the price of the asset increases beyond the strike price of the call option, the profit is capped at that strike price, minus the premium received. If the price declines, losses on the asset are partially offset by the option premium.