$33 \cdot 219^{89}+89^{19}$ The unit digit is
(A) 0 .
(B) 2 .
(C) 8 .
(D) 9 .
(1st "Five Sheep Cup" Junior High School Mathematics Competition, 1989)
[Solution] When $n$ is odd, the last digit of $9^{n}$ is 9, denoted as $\left\langle 9^{n}\right\rangle=9$. Thus, $\left\langle 19^{89}+89^{19}\right\rangle=\left\langle 19^{89}\right\rangle+\left\langle 89^{19}\right\rangle=\langle 9+9\rangle=8$. Therefore, the answer is $(C)$.