What is the optimal method for a developer to troubleshoot this?

An Apex trigger creates an Order__c record every time an Opportunity is won by a Sales Rep. Recently the trigger is creating two orders.

What is the optimal method for a developer to troubleshoot this?
A . Set up debug logging for every Sales Rep, then monitor the logs for errors and exceptions.
B . Turn off all Workflow Rules, then turn them on one at time to see which one causes the error.
C . Add system.debug() statements to the code and use the Developer Console logs to trace the code.
D . Run the Apex Test Classes for the Apex trigger to ensure the code still has sufficient code coverage.

Answer: C