Using which of the following is considered deadly force?

A knife is considered a deadly force because it has the potential to cause serious injury or death when used against another person. The classification of force as "deadly" typically refers to whether the method can reasonably be expected to cause death or serious bodily harm. Knives, due to their design and purpose, can easily inflict fatal injuries.

In contrast, while a baton and a stun gun can certainly cause harm, they are generally not classified as deadly force unless used in a manner that could foreseeably lead to death. Firearms are also categorized as deadly force due to their capacity to inflict fatal wounds; however, in this context, the focus is on the knife as the correct response, highlighting its inherent lethal potential in confrontational situations.