The correct answer is (D) A ruse; a scheme or trick to surprise or deceive an adversary; a ploy devised to attain a goal or gain an advantage over another person. Any artifice or trickery to deceive another.

Stratagem comes from French stratagème, Greek stratègèma.

Examples of use:

• Spammers use a variety of stratagems in an effort to infect other computers.
• The use of the Trojan wooden horse was one of history's great stratagems.