$$
\begin{array}{l} 
11 \cdot 13 \text { If }(3 x-1)^{7}=a_{7} x^{7}+a_{6} x^{6}+\cdots+a_{0} \text {, then } a_{7}+a_{6}+ \\
\cdots+a_{0} \text { equals }
\end{array}
$$
(A) 0 .
(B) 1 .
(C) 64 .
(D) -64 .
(E) 128 .
(28th American High School Mathematics Examination, 1977)
[Solution] The sum of the coefficients of the polynomial $p(x)=\sum_{k=0}^{n} a_{k} x^{k}$ is $\sum_{k=0}^{n} a_{k}$, which equals $p(1)$, so $a_{7}+a_{6}+\cdots+a_{0}=(3 \cdot 1-1)^{7}=128$. Therefore, the answer is $(E)$.