1. Un día de primavera, Antonio y Alicia [viajaron] (viajar) por el campo.
2. [Hacía] (hacer) mucho sol.
3. El cielo [estaba] (estar) azul.
4. Todo se [veía] (ver) muy bonito.
5. De repente, ellos [oyeron] (oír) una explosión.
6. El auto [empezó] (empezar) a temblar.
7. Antonio lo [paró] (parar), y ellos [se bajaron] (bajarse).
8. [Querían] (querer) saber qué pasó.
9. Inmediatamente, ellos [vieron] (ver) que se había pinchado una llanta.

1. Pret: The key phrase is "one day." They traveled once.
2. Imp: The weather is often a background description.
3. Imp: background description/weather
4. Imp: background description. Background descriptions also create the setting for the story.
5. Pret: They heard the explosion once. It was not a regular occurrence. Hearing an explosion which uses imperfect might only apply to someone who lives/lived in a war-zone or by a mine.
6. Pret: This focuses on the beginning, and it occurred once.
7. Pret: occurs once; Pret: occurs once
8. Imp: "They wanted to." By contrast, "querer" in preterite means "to try." (See the second part of 8.2 on the course website.)
9. Pret: "Inmediatamente" is a strong indicator that the preterite should be used. The action occurs once.