Consider the network shown below. Suppose AS$1$ and AS$2$ are running OSPF for their intra$-$AS routing protocol. Suppose AS$3$ is running RIP for its intra$-$AS routing protocol. Suppose eBGP and iBGP are used for the inter$-$AS routing protocol. Let $x$ be a new prefix added to the network as shown at Router $1$a$.$

$($a$)$ Router $1$c learns about prefix $x$ from which routing protocol: OSPF, RIP, eBGP, or iBGP?

$($b$)$ Router $2$a learns about $x$ from which routing protocol?

$($c$)$ Router $2$c learns about $x$ from which routing protocol?

$($d$)$ Router $3$a learns about $x$ from which routing protocol?