The correct answer is: A. Call option.
A call option is a contract that gives the buyer the right, but not the obligation, to buy a specified amount of an underlying asset at a specified price on or before a specified date. The seller of the call option, also known as the option writer, is obligated to sell the asset if the buyer exercises the option.
A put option is a contract that gives the buyer the right, but not the obligation, to sell a specified amount of an underlying asset at a specified price on or before a specified date. The seller of the put option, also known as the option writer, is obligated to buy the asset if the buyer exercises the option.
A double option is a combination of a call option and a put option. The buyer of a double option has the right to buy or sell the underlying asset at a specified price on or before a specified date. The seller of the double option is obligated to buy or sell the asset if the buyer exercises the option.
A single option is a contract that gives the buyer the right, but not the obligation, to buy or sell a specified amount of an underlying asset at a specified price on or before a specified date. The seller of the single option, also known as the option writer, is obligated to buy or sell the asset if the buyer exercises the option.