A large message of $1$ Mbits is transmitted over two hops. The

transmission line in each hop has a bit error rate of BER$={10}^{-6}.$ The

number of bits needed to get $2$ Mbits across the first hop correctly is

approximately:

$($a$)1$ Mbits $($b$)2$ Mbits

$($c$)4$ Mbits $($d$)3$ Mbits