plot line utilization as a function of P$,$ the probability that a single frame is in error for the following error$-$ control techniques: a$.$ Stop$-$and$-$wait b$.$ Go$-$back$-$N with W $=7$ c$.$ Go$-$back$-$N with W$=127$ d$.$ Selective reject with W$=7$ Selective reiect with W$=127$