$13 \cdot 61$ If the sum of 7 consecutive even numbers is 1988, then the largest one among these 7 numbers is
(A) 286.
(B) 288.
(C) 290.
(D) 292.
(China Junior High School Mathematics Correspondence Competition, 1987)
[Solution] Let the 7 consecutive even numbers be
$$
2 n-6,2 n-4,2 n-2,2 n, 2 n+2,2 n+4,2 n+6 \text {. }
$$

Thus, we have $(2 n-6)+(2 n-4)+(2 n-2)+2 n+(2 n+2)+(2 n+$
4) $+(2 n+6)=1988$,

which simplifies to $14 n=1988$, giving $n=142$.
Then $2 n+6=284+6=290$.
Therefore, the answer is $(C)$.