* Cuando ellos subieron al segundo piso, ¡se encontraron en una fiesta de sorpresa para Toño!
Explanation:
Because an action performed in the past tense is being described that does not yet have its definite end, so it is important to identify the person, gender, time and number in the sentence in this way it is possible to correctly conjugate the verb in the sentence and have coherence with what is being expressed.
