Solution
= Solution
{c}
Take $a=[x]$. Every <quotient> class is a <polynomial> expression in $a$ with coefficients from $F$, so $K=F[a]$. Substitution gives $f(a)=[f(x)]=0$. Thus
$$
\boxed{K=F[a],\qquad f(a)=0.}
$$
This constructs a <field> containing a root even when no root existed in the original <field>.