How many spare life vests are stored in the forward overhead bin (FWD OHB)?

The correct answer is based on the standard safety equipment protocols that require specific quantities of life vests to ensure passenger safety during emergency situations. In the context of an aircraft, having four spare life vests stored in the forward overhead bin ensures that there are enough additional vests to accommodate unforeseen circumstances, such as extra passengers or situations where a vest may be compromised. This number is aligned with regulatory requirements that emphasize the importance of preparedness and the safety of all individuals on board.

While other options suggest fewer vests, the choice of four reflects an adherence to safety standards designed to equip the aircraft adequately for emergencies, ensuring that the crew can provide for all passengers in need. The emphasis on having a sufficient number of vests directly correlates to the commitment to safety in aviation practice, which is why this answer is the most suitable.