Answer:
The right conjugation of the verb between parentheses is:
- Susana y yo fuimos los mejores estudiantes el semestre pasado. 
 - ¿Por qué fuiste muy antipático ayer?
 - La señora Pérez no fue muy simpática con nosotros ayer.
 - ¿Cómo fueron los programas?
 - Yo fui estudiante de medicina, pero decidí estudiar arquitectura. 
 - Yo fui de compras anoche.
 - Cuando contesté su pregunta... ¡Uy, fui muy estúpido!
 - ¿Cuándo te fuiste de vacaciones?
 - Mis compañeros de cuarto fueron a clase. 
 - Los niños fueron a su cuarto, pero no se acostaron.
 
Step-by-step explanation:
The translation of the sentences is:
- Susana and I were the best students last semester. 
 - Why were you very unfriendly yesterday? 
 - Mrs. Pérez was not very nice to us yesterday. 
 - How were the programs? 
 - I was a medical student, but I decided to study architecture. 
 - I went shopping last night. 
 - When I answered your question ... Oops, I was very stupid! 
 - When did you go on vacation? 
 - My roommates went to class. 
 - The children went to their room, but did not lie down.
 
In Spanish there is a possible confusion due to the conjugation in Preterite of the verbs "ser" and "ir", since they are the same, but you must remember the use of each of these verbs:
- "Ser" It is used to mention everything that is a noun, be it its appearance or mental qualities. 
 - "Ir" is used to mention the place to which the noun is directed.
 
Taking into account the following, I show you the possible conjugations of these verbs in their Preterite Form:
- Yo fui.
 - Tú fuiste.
 - Usted fue.
 - Él fue.
 - Ella fue.
 - Ello fue.
 - Nosotros fuimos.
 - Ustedes fueron.
 - Ellos fueron.
 
Finally, you just have to replace the noun with your personal pronoun and use the necessary conjugate form.