Answer:
Every sentence should be completed the following way:
1- Yo COMPRÉ los ingredientes antes.
2- Todos nosotros los PREPARAMOS durante la clase.
3- Carlos y Alfredo PREPARARON los camarones para la parrilla.
4- José CALENTÓ el agua para el arroz.
5- Silvia AÑADIÓ una pizca de sal y pimienta negra a todo.
In Spanish, the preterit tense is strictly limited, in its use, to contexts in which the action carried out is found in a clear and indisputable past with respect to the moment of enunciation, such as in past simple in English. On the contrary, a story will be formulated with the use of the imperfect tense.