What can you infer from the facts that PROBLEM-A is NP-complete and PROBLEM-A linear-time reduces to PROBLEM-B? $C_1$: If there exists an $O(N^3)$ algorithm for PROBLEM-B, then $P=NP$. $C_2$: If there does not exist an $O(N^3)$ algorithm for PROBLEM-B, then $P\ne NP$. $C_3$: If there exists an $O(N^3)$ algorithm for PROBLEM-B, then there exists an $O(N^3)$ algorithm for PROBLEM-A. $C_4$: If there exists an $O(N^3)$ algorithm for PROBLEM-A, then there exists an $O(N^3)$ algorithm for PROBLEM-B.