Son las nueve de la mañana
It's describing the chica, which is singular and also feminine, so therefore we must use la.
1. nadie va al laboratorio
2. ella no presta atención tampoco
3. no aprenden nada de memoria
4.no hay ni unas sillas en la sala
5. nunca llevas el carnet the identidad
Disclaimer this is my understanding and i’m not 100% sure but i hope you do well!
Why is it in Spanish tho?
"participaban" should be in the blank.