Final answer:
The most commonly used method for greasing a glass pie pan when baking a pie crust is spraying with cooking spray for its convenience and effectiveness.
Step-by-step explanation:
When baking a pie crust in the oven, the commonly used method for greasing a glass pie pan is B. Spraying with cooking spray. This method provides a quick, even coating that helps to prevent the pie crust from sticking to the pan. Alternatively, some bakers also prefer A. Buttering the pan using softened butter, as it can add flavor and a rich texture to the crust. While C. Using parchment paper and D. Dusting with flour are other methods, they are less common for pies compared to other baked goods. Overall, cooking spray is favored for its convenience and effectiveness.