Select the correct statement$($s$)$ regarding $4$B$5$B$.$

a$.$ a four bit dataword is mapped to a $5$ bit codeword; this results in only half of the possible codewords being mapped to legitimate datawords

b$.4$B$5$B means that only $80\%$ of the codeword represents information, with $20\%$ representing overhead

c$.4$B$5$B avoids long string of logical $1$s$$ and $0$s$,$ thus enabling use of simpler line coding techniques

d$.$ all statements are correct