Which of the Following Is NOT a Valid Rule of Thumb

Which of the following is NOT a valid rule of thumb on risk control strategy selection?

A) When a vulnerability exists: Implement security controls to reduce the likelihood of a vulnerability being exploited.
B) When a vulnerability can be exploited: Apply layered protections, architectural designs, and administrative controls to minimize the risk or prevent the occurrence of an attack.
C) When the attacker's potential gain is less than the costs of attack: Apply protections to decrease the attacker's cost or reduce the attacker's gain, by using technical or operational controls.
D) When the potential loss is substantial: Apply design principles, architectural designs, and technical and non-technical protections to limit the extent of the attack, thereby reducing the potential for loss.