Final answer:
The most effective revision is option C, which uses a semicolon and 'however' to emphasize the contrast between the belief in changelings as a harmless superstition and the actual harm it sometimes caused.
Step-by-step explanation:
The best way to revise and combine the underlined portion of the sentences is by using the option C. 'an innocuous superstition; however, on some occasions,' This option effectively contrasts the idea that the belief in changelings was merely a harmless superstition with the reality that it sometimes led to harm. The use of the semicolon followed by 'however' provides a clear and strong transition that emphasizes the contrast between the two parts of the sentence.
The best way to revise and combine the underlined portion of the sentences is option C: an innocuous superstition; however, on some occasions. This option effectively combines the two ideas, indicating that the belief in changelings being convinced to leave is generally harmless, but there are instances when harm can occur. The use of 'however' clarifies the contrast between the innocuous nature of the belief and the potential harm that can result.