Most PPP implementations use an abbreviated form that skips unnecessary information. LCP handles address and control field information during the link setup. As a result, which of the following fields and values are found in the PPP header and trailer? $($Choose all that apply.$)$

a$.$ Flag, a single$-$byte field.

b$.$ Frame Check Sequence $($FC$),$ a two$-$byte field.

c$.$ Protocol identifier $($PID$),$ a two$-$byte field.