Question

My parents (listened/were listening) to the radio when I came into the kitchen

Answer 1

 were listening to the radio      

Answer 2

Both "listened" and "were listening" are grammatically correct in this context, but the choice depends on the intended meaning and the context of the situation.

If you use "listened," it implies that your parents were already listening to the radio when you came into the kitchen, and they might have stopped listening after you arrived.

If you use "were listening," it implies that your parents were in the middle of listening to the radio when you entered the kitchen, and they continued to listen even after you arrived.

So, the choice between "listened" and "were listening" depends on the specific nuance you want to convey in the sentence.