According to the Transaction Thresholds document1, you can set static thresholds for individual business transactions by selecting Individual Transaction Thresholds from the Business Transaction Configuration window. You can then specify the values for Slow, Very Slow, and Stall thresholds for each business transaction. This way, you can customize the thresholds according to the SLA and the expected performance of the long-running transactions. Setting the default thresholds or adjusting the health rules would affect all the business transactions, not just the long-running ones. Therefore, the correct answer is C. References:

Transaction Thresholds