3. Given that the units digit of $2^{n}+7^{n}(n \in \mathbf{N}, n>2010)$ is 3. Then the smallest $n$ is ( ).
(A) 2011
(B) 2012
(C) 2013
(D) 2014
3. D.

Notice that the units digit of $2^{k}$ cycles through $2, 4, 8, 6$, while the units digit of $7^{k}$ cycles through $7, 9, 3, 1$.

Since the units digit of $2^{n}+7^{n}$ is 3, it follows that $n$ is of the form $4k+2$.
Given that $n>2010$, the smallest $n$ is 2014.