1. In a certain table tennis singles competition, it was originally planned that each pair of players would play exactly one match, but after three players each played two matches, they withdrew from the competition, and as a result, only 50 matches were played in total. The number of matches played among these three players is ( ).
A. 0
B. 1
C. 2
D. 3
1. B. From the problem, we get $50=C_{n-3}^{2}+(3 \times 2-r)$, where $r$ is the number of matches played among the 3 players, i.e., $(n-3)(n-4)=88+$ $2 r$. Only when $r=1$ does $n=13$ become a positive integer, hence the answer is B.