2. The unit digit of $2+2 \times 3+2 \times 3 \times 3+2 \times 3 \times 3 \times 3+\cdots+2 \times \underbrace{3 \times \cdots \times}_{9 \text { } 3} 3$ is
A. 2
B. 8
C. 4
D. 6
Analysis: Number Theory, Periodic Digit Problem.
Original expression $=2 \times\left(1+3+3^{2}+3^{3}+\cdots+3^{9}\right), 3^{\mathrm{n}}$'s unit digit appears in a cycle of $3, 9, 7, 1$, 3+9+7+1=20, $9 \div 4=2 \cdots 1$, so the unit digit of the original expression is $2 \times(1+20 \times 2+3) \equiv 2 \times 4=8(\bmod 10)$, so the answer is $B$.