Richard's actual motivation for not selling Betsy the dog is not explicitly provided in the given references; thus, the answer to the question is not apparent from the options A, B, or C. Hence the correct option is D.
The student's question appears to be asking for the motivation of a character named Richard for not selling a dog named Betsy in literature. Without a text explicitly stating Richard's motivation, it is difficult to provide a definitive answer.
The provided texts discuss different themes such as the cruelty of an enslaver, living in free states, families being torn apart, loyalty, and complex human emotions, but do not directly address Richard's situation with Betsy the dog. Therefore, based on the provided references, Richard's motivation seems to be more complex and is not covered by the options A, B, or C.
Hence the correct option is D.