A would be wrong since eres is are and I are Mexican wouldn’t make sense. Tú eres Mexicano would make sense.
B is also wrong since estás means are you. For example:¿ estás en Camino? Are you on your way? Therefore B is wrong
D is also wrong since estoy is in the yo form but it is used incorrectly. An example sentence of this would be: Estoy en Camino. I am on my way. Estoy means I am.
This leaves C as the correct answer since soy mean am. You soy Mexicano is correct.
1. in Spain there is two main parades which appear Sunday & Tuesday in late July or June 2. visit Barcelona it has Gaudi buildings & Majorca it has mountain villages 3. Madrid it is a royal palace & a muesum