7.107 If $f(a)=a-2$ and $F(a, b)=b^{2}+a$, then $F[3, f(4)]$ is
(A) $a^{2}-4 a+7$.
(B) 28 .
(C) 7 .
(D) 8 .
(E) 11 .
(4th American High School Mathematics Examination, 1953)
[Solution] Given $F[3, f(4)]=[f(4)]^{2}+3=(4-2)^{2}+3=7$. Therefore, the answer is $(C)$.