What term is used to describe singing without instruments or accompaniment?

Question: What term is used to describe singing without instruments or accompaniment?

Options:

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Correct answer:

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7 little words

1. Copies another’s work
2. Fields for grazing
3. Little Women star Winona
4. Wince in embarrassment
5. Receiving for work
6. Loud New World monkeys
7. Like filled hard-boiled egg