1. Ustedes (gastar, oír) la explosión anteayer.
You (to waste, to hear) the explosion the day before yesterday.
2. ¿(asistir, decidir) tú a la clase de inglés?
Did you (to attend, to decide) the English class?
3. Anoche Lucía (ver, jugar) una película interesante.
Last night Lucía (to see, to play) an interesting movie.
It looks like we have to choose the correct infinitive and then conjugate it according to the given subject and the tense.
For 1), "to hear" makes more sense than "to waste". The subject is ustedes and the tense is preterite. The conjugation of oír for the subject ustedes in the preterite tense is oyeron.
For 2), "to attend" makes more sense than "to decide". The subject is tú and the tense is preterite. The conjugation for the subject tú in the preterite tense is asististe.
For 3), it may seem like both make sense, but "to see" makes more sense than "to play" because to say "to play the movie" in Spanish, you would say poner la película. The subject is Lucía (which means we will use the conjugation for the subject ella) and the tense is preterite. The conjugation for the subject ella in the preterite tense is vio.
Answer:
1. oyeron
2. asististe
3. vio
1. Ustedes oyeron la explosión anteayer.
2. ¿Asististe tú a la clase de inglés?
3. Anoche Lucía vio una película interesante.