Answer: C) to illustrate the unique beauty found in China.
Step-by-step explanation: When writing, an author can have several different purposes, for example: to persuade, inform, to entertain, to explain, etc. From the given options, the one that represents the author's purpose for writing the text, is the corresponding to option C: to illustrate the unique beauty found in China, because, as we can see, the narrator describes the mules as "enormously tall, enormously heavy, very beautiful beasts, white, red, yellow, and black, and sleek with unlimited polishing and grooming."