What vehicle part prevents the window glass from falling to the bottom of the door?

The part that prevents the window glass from falling to the bottom of the door is the track channels and stop block. Track channels guide the movement of the window glass as it is raised or lowered, ensuring it stays properly aligned within the door frame. The stop block plays a crucial role by limiting how far the window can descend, effectively preventing it from falling completely out of the door. This mechanism is essential for both safety and functionality, as it keeps the window securely in place while allowing for its intended movement.

The other options, while they may reference aspects of the window operation, do not fully capture the complete function combined with the mechanism that supports the window glass. For instance, the mention of power windows channels block fails to describe the operational guidance necessary for the window's movement. Similarly, stop block channels and window regulator, track channel, do not collectively address both the guidance and safety aspects that the track channels and stop block provide. Therefore, the combination of track channels and stop block accurately describes the design and purpose of preventing the window from falling.