To Which of the Following Two-Object Systems Can We Apply $C$

Short Answer

To which of the following two-object systems can we apply conservation of momentum, and why? In each case, answer "A" if we can apply conservation of momentum because the system floats in space, "F" if it's because the system is functionally isolated, " $C$ " if it's because the system undergoes a collision, and " $\mathrm{D}$ " if momentum is not conserved at all because the system is not isolated.
-Two magnetic hockey pucks slide on a flat plane of frictionless ice. They attract each other as they pass, changing each other's trajectories without touching.