Consider the network shown below. Suppose AS$3$ and AS$2$ are running OSPF for their 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 inter$-$AS routing protocol. Initially suppose there is no physical link between AS$2$ and AS$4.$

a$.$ Router $3$c learns about prefix $x$ from which routing protocol: OSPF, RIP, eBGP, or iBGP?

b$.$ Router $3$a learns about $x$ from which routing protocol?

c$.$ Router $1c$ learns about $x$ from which routing protocol?

d$.$ Router $1$d learns about $x$ from which routing protocol?