You work as an application developer at Certkiller .com. Certkiller .com uses an application that calculates monthly payments based upon client input. You are currently debugging this application using the Microsoft Visual Studio 2005 IDE. The application contains the following code：  public double CalculateMonthlyPayment （Single rate， double principal） {  //Implementation code }  You have discovered that unexpected results are being returned by the application. You would like to pause execution and display a message box containing an error message in the event of a negative or zero rate value is Passed to the CalculateMonthlyPayment method.  You need to ensure that this only occurs during debugging mode. What should you do？（）

• A、A
• B、B
• C、C
• D、D