3. Observe the following equations:
$$
\begin{array}{l}
3^{1}=3,3^{2}=9,3^{3}=27,3^{4}=81, \\
3^{5}=243,3^{6}=729,3^{7}=2187, \cdots
\end{array}
$$

Then the last digit of $3+3^{2}+3^{3}+3^{4}+\cdots+3^{2014}$ is ( ).
(A) 2
(B) 3
(C) 7
(D) 9
3. A.

From the given equation, it is easy to know that the last digit repeats every four numbers. Since $2014=4 \times 503+2$, we have
$$
3+3^{2}+3^{3}+3^{4}+\cdots+3^{2014}
$$

the last digit is equivalent to that of
$$
3+9+7+1+\cdots+9
$$

which is 2.