This is the last one. Suppose AS$3$ and AS$2$ are running off OSPF for the intra$-$AS routing protocol. Suppose AS$1$ and AS$4$ are running RIP for their intra$-$AS routing protocol. Suppose EBGP and IBGP are used for the intra$-$AS routing protocol. Initially, suppose there is no physical link between AS$2$ and AS$4.$ Router $4$B learns about Prefix X from which routing protocol? OSPF, RAP, EBGP, or IBGP.