Question

Her friends are listening and some of them ........ ( sing ) ........ Along.

Answer 1

Her friends are listening and some of them are singing along.

It’s because it has to be parral structure and it’s not a past tense to it’s are and not were

I hope this helps you understand ((:

Answer 2

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are singing

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Since, in the sentence we can see that the action is continuing. Hence its present continuous tense.

The above sentence is about present continuous. Here two actions are happening. One is "listening" and the other is "are singing".

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