The correct answer is D) Shutdown the engine and troubleshoot. If the lube oil scavenge temperature exceeds 300 degrees Fahrenheit on a gas turbine engine, and reducing power does not bring the temperature within limits, the operator should shut down the engine and troubleshoot the issue. This is because an excessively high lube oil temperature can indicate a serious problem with the engine, such as a malfunctioning component or lack of proper lubrication. Continuing to operate the engine in this condition could lead to catastrophic failure. The safest and most appropriate action is to shut down the engine and thoroughly inspect and repair the issue before attempting to restart it. The other options are incorrect because they do not address the severity of the situation. Continuing to operate at a reduced power level or simply monitoring the temperature could allow the problem to worsen and potentially cause engine damage. Further reducing power may not be sufficient to bring the temperature within acceptable limits.