Which of the following is not an acceptable way to check your blind spots?

Checking the blind spots is crucial for safe driving, as these areas are not visible in your vehicle's mirrors. The correct method that is not acceptable for checking blind spots involves looking at the rear seats. While checking the back seats may provide information about passengers or cargo, it does not help in identifying vehicles or obstacles in your blind spots.

In contrast, looking over your shoulder is a commonly accepted technique to physically check blind spots. It allows you to see areas that mirrors cannot cover. Using side mirrors is also important, as they can help to monitor areas adjacent to your vehicle, but they can still have limitations. Adjusting your rearview mirror helps you to see directly behind your vehicle but does not aid in observing the sides or blind spots. Each of these methods (looking over your shoulder, using side mirrors, and adjusting the rearview mirror) is designed to enhance awareness and safety when changing lanes or merging.