Which of the following is NOT one of the three safeties in a Glock?

The manual safety is not one of the three safeties in a Glock. Glocks are designed with a unique safety system that includes a trigger safety, a firing pin safety, and a drop safety. The trigger safety is a lever integrated into the trigger that must be engaged for the trigger to move and thus prevent accidental discharge. The firing pin safety is a mechanism that blocks the firing pin unless the trigger is pulled, preventing unintentional firing. The drop safety ensures that the firearm cannot discharge if dropped.

The absence of a manual safety lever is a significant design feature of the Glock platform, which promotes a consistent trigger pull without additional manual operations required by the user. This design choice prioritizes the ease of use and readiness of the firearm, making the manual safety an option that is not present in Glocks.