$28 \cdot 22$ Let $N$ be a number between 9 and 17. If the average of 6, 10, and $N$ is an even number, then it can only be
(A) 8.
(B) 10.
(C) 12.
(D) 14.
(E) 16.
(5th American Junior High School Mathematics Examination, 1989)
［Solution］According to the problem, it is obvious that (let $\bar{x}$ be the average of the three numbers)
$$
\frac{9+6+10}{3}<\bar{x}<\frac{17+6+10}{3} \text {, }
$$

which means
$$
8 \frac{1}{3}<\bar{x}<11 \text {. }
$$

Thus, $\bar{x}=10$.
Therefore, the answer is $(B)$.