Answer :
Answer:
c. a difference in the subject matters of operas X and Y
Explanation:
All factors could directly explain the fact that opera Y generated far greater net profits that did opera X except for this one. Although the subject matter might have some impact on sales, it could not do so in a direct way. It could only do so if we take other factors into account, such as the cost of producing a particular opera or the interest that people have on an opera (which results in greater or lesser ticket sales).