The answer is <u>sonó</u>
Yo me duchaba cuando <u>sonó</u> el teléfono.
The verb duchaba is in pretérito imperfecto and matches with simple past (in this case sonó). This pretérito imperfecto describes an action or state in the past, without indicating whether it was completed or not.
Hice una fiesta
Tomamos muchos
Estudiamos mis amigos y yo
Lo pasamos genial
Estuvimos en la piscina
The words “ser” and “estar” mean to be
B because you need the past tense of tú
The Americans would pay millions of dollars to defend their country, but not 1 cent towards the bribe in response to the XYZ affair. Hope this helps! :)