1.Bailamos
2.Estudian
3.camino
4.compra
5.cantan
6.hablas
7.pagamos
8.necesita
9.usan
The correct answer would be: Cuando _X_ lavo el coche, no uso detergente.
Good luck!
“Se compran zapatos” this sentence makes sense bc it’s a neutral. Meaning that is not directly to someone or something