Well there's no list but i can tell you to look for something similar to this "tengo muchas ganas de viajar" or "en serio, quiero viajar"
The answer is son because son means are
Ellos iban a la escuela
Here the imperfect tense is iban which means were going
El dormía tarde ayer
Here the imperfect tense is dormía which means slept
Nosotros hablábamos por teléfono
Here the imperfect tense is hablábamos which means we were talking
Ellas iban al centro comercial
Here the imperfect tense is iban which means were going
