B$.$ Give at least three reasons why IP does reassembly at the destination host rather than within routers. $(4$ points$)$

C$.$ Suppose that a TCP message containing $2048$ bytes of application data and a $20$ byte TCP header is passed down to IP for delivery across two networks $($from the source host to a router to the destination host$).$ The message, as it is passed down from TCP to IP$,$ would look like this: