Answer: Jamie and his friends (sing/sings) at a Christmas party.
Step-by-step explanation:
In the present tense, when the subject (noun) is singular, we use the"plural" form of the verb which is added -s at the end.
In the present tense, when the subject (noun) is plural, we use the "singular" form of the verb which is the original verb.
In past tense, singular and plural have the same kind of verb.
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Therefore, since "Jamie and his friends" is plural, we use the original verb, which is sing.
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