Though the way the questions are worded can be tricky and lead to a wrong answer would not completely understood. Let's try a practice question and see how you do. When replacing an external fuel filter, best practices include what? A, use the same brand as the original replacement filter. B, reuse the filter after cleaning. C, relieve fuel system pressure before removing the fuel line connections. D, tighten fasteners as tight as possible. The correct answer is C. The fuel lines are under pressure even after the engine has been turned off. This is necessary to spray the fuel into the combustion chamber of your vehicle in the correct amount at the right time and for easier engine restarts. Relieving that pressure is an important safety step before attempting a fuel filter replacement.