The answer is A. El
Ellas has to do with girls (plural)
Las is a feminine item and plural and its not la either
it wont let me add my answer because its inappropriate even though it doesn't have any curse words or inappropriate words?
Answer
1. Tú
2. El
3. Usted
4. Ella
5. Nosotros
6. Vosotros (spain)
7. Ellos
8. Ellas
9. Yo
10. Ellos
11. Ellos
12. Nosotros
13. Ellos
14. Vosotros (spain)
15. Ellas
16. Nosotros
17. El