The correct answer is (A) To make a soft, vibratory murmur. To utter a continuous, low, vibratory sound expressive of satisfaction, as does a cat or other feline animal. To express as if by purring.

Purr comes from the sound itself.

Examples of use:

• The engine of the heavy automobile purred as they sped down the highway.
• The cat purred contentedly as it lay beside its mistress.