Final answer:
The test approach where old and new systems operate simultaneously in all locations is known as parallel testing, which is a form of risk management during system implementation.
Step-by-step explanation:
When old and new systems operate simultaneously in all locations as a test approach, it is known as D) parallel testing. This method is particularly effective for validating new systems against their older counterparts by comparing their outputs in a real-world environment. This serves as a risk management strategy because it allows for the validation of new system functionality without disrupting the current processes that the old system supports.
By conducting parallel tests, organizations can identify discrepancies and ensure that the new system performs as expected before fully replacing the legacy system. This process aligns with the principle of approaching a problem from multiple directions to promote greater flexibility and validation, much like the multiple working hypotheses strategy used in scientific research.