Through my research I found questions similar to this with answer choices:
A) medicinal material excreted by macrophages
B) the death of macrophages
C) pathogens trying to infect the area
D) blood cells losing their hemoglobin
The best answer among the following choices would be the second option aka B) The death of Macrophages because cutting your knee is cutting your skin since something sharp went through the layers it basically killed things in order to get to you, to make you feel the pain, so as a result of the cut, it killed the macrophages, which are like your security system for your immune system that protects you, but the cut broke through and harmed the skin.