3. Let $N=3^{1001}+7^{1002}+13^{1003}$. Then the units digit of $N$ is ( ).
(A) 3
(B) 6
(C) 9
(D) 0
3. C.

Since the unit digit of $3^{1001}$ is 3, the unit digit of $7^{1002}$ is 9, and the unit digit of $13^{1003}$ is 7, therefore, the unit digit of $N$ is 9.