Определить функцию окончания S

4. The scientist made important discoveries in mathematics.
5. This laboratory assistant makes interesting experiments.
6. Everybody knows about this scientist’s interest in electricity.
7. He carries out physical experiments.
8. The professor lectured at the University more than 10 years ago.
9. My sister’s favorite subject at school was English.
10. Today he begins to work at our laboratory.
11. We found some interesting articles on chemistry.