The correct response that describes how to demonstrate conservation of momentum in a system of two moving particles that collide is:
Determine the momentums of the two particles before the collision and add them together. Determine the momentums of the two particles after the collision and add them together. Verify that both sums are the same.
This choice correctly outlines the conservation of momentum by comparing the total momentum before and after the collision, which should be equal if momentum is conserved.