10. Three inhabitants of the planet Zog met in a crater and counted each other's ears. Imi said, "I can see exactly 8 ears"; Dimi said, "I can see exactly 7 ears"; Timi said, "I can see exactly 5 ears". None of them could see their own ears. How many ears does Timi have?
A 2
B 4
C 5
D 6
E 7
10. C The aliens say they can see $8,7,5$ ears respectively, but each ear has been seen by two aliens so is counted twice. Hence the total number of ears is $\frac{1}{2}(8+7+5)=10$ ears. Each alien can see all ten ears, except its own. Timi sees 5 ears, so has $10-5=5$ ears.