Quiz: Recognizing 2-SAT

A problem says: "You have $n$ items, each colored red or blue. Some pairs must be different colors." Can you model this as $2$-SAT?

1. A.No, because $2$-SAT only handles implications, not difference constraints
2. B.No, because this requires $3$ or more colors
3. C.Yes. For each pair $(i, j)$, add $(x_i \lor x_j)$ and $(\neg x_i \lor \neg x_j)$
4. D.Yes, but only if the underlying graph is bipartite