In this task, find the most appropriate number to replace the blank (indicated with _ ) and express it in words.

Q: Plants have many white flowers with _ petals, giving the plant a white, flat-topped appearance.

A: four
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Q: Conserved residues make similar contacts in _ repressor-operator complexes.

A: two
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Q: Harmony occurs when _ or more sounds are heard simultaneously.

A:
two
****