7・91 Let $f(x)=a x^{4}-b x^{2}+x+5$, and $f(-3)=2$, then $f(3)$ equals
(A) -5 .
(B) -2 .
(C) 1 .
(D) 3 .
(E) 8 .
$$
\begin{aligned}
\text { [Solution] } \quad f(-3) & =a(-3)^{4}-b(-3)^{2}+(-3)+5 \\
& =a \cdot 3^{4}-b \cdot 3^{2}+2, \\
\because \quad f(-3)= & 2, \quad \therefore a \cdot 3^{4}-b \cdot 3^{2}=0 . \\
\therefore \quad & f(3)=a \cdot 3^{4}-b \cdot 3^{2}+3+5=8 .
\end{aligned}
$$

Therefore, the correct choice is $(E)$.