A7. Does the equation $9^{n}+9^{n}+9^{n}=3^{2007}$ have an integer as a solution?
(A) yes, $n=667$
(B) yes, $n=669$
(C) yes, $n=1003$
(D) yes, $n=2006$
(E) no
A7. $9^{n}+9^{n}+9^{n}=3 \times 9^{n}=3 \times 3^{2 n}=3^{2 n+1}$. So $n=1003$. (C).