Final answer:
The correct phrase to complete the sentence is 'OD. se divirtieron'. 'Se divirtieron' is the correct conjugation of the verb 'divertir' to match the subject 'mis amigos'.
Step-by-step explanation:
The correct phrase to fill in the blank is OD. se divirtieron.
In this sentence, 'mis amigos' is the subject and 'se divirtieron' is the correct conjugation of the verb 'divertir' in the past tense to match the subject. The verb 'divertir' means 'to have fun'.
Example: 'Mis amigos se divirtieron mucho en la fiesta anoche' means 'My friends had a lot of fun at the party last night'.
Learn more about Verb conjugation in Spanish