$35 \cdot 14$ In a math competition, 100 students from a school participate, among whom there are at least 9 girls. It is also known that in any group of 10 participants, there is at least 1 boy. Then the number of boys participating in the competition is
(A) 89.
(B) 91.
(C) 82.
(D) 63.
(1st "Five Sheep Cup" Junior High School Math Competition, 1989)
[Solution] If there are 10 girls, then there would be no boys among them, which contradicts the problem statement. Therefore, the number of girls is exactly 9, meaning there are 91 boys. Hence, the answer is $(B)$.