Correct Answer: Cadence

Solution : The correct choice is the third option.

The most appropriate one-word substitution for the group of words "rhythmic flow of sounds or words" is cadence, which refers to a rhythmic flow or modulation of sounds or words, often in speech or music. It involves the rise and fall of the voice in a sequence, creating a sense of rhythm or melody.

The meanings of the other options are as follows:

• Credence: This term refers to belief in or acceptance of something as true.
• Crescents: This term refers to the curved shape, like that of a crescent moon.
• Copious: This term means abundant.

Therefore, the correct substitute for the given group of words is cadence.