Which listing NEVER receives a push when alone?

• A. Pi
• B. As
• C. In
• D. Ex

Answer: (D)

In this system, a listing describes the direction a vertebra is displaced, and a push is a direct thrust along that direction to reposition it. One particular listing is defined in a way that a single, straight push isn’t used for it when it appears alone. The reason is that its correction relies on how forces combine with other vectors or contacts; a standalone push along that direction wouldn’t produce the correct, stable adjustment and can even be destabilizing. Instead, this listing is effectively addressed only when it accompanies other listings or through a different contact strategy that couples with other movements. Because of that, you never apply a direct push to this listing on its own. The other listings, by contrast, align with a straight line of drive that can be corrected with a solitary thrust, so they do receive a direct push when encountered by themselves. Therefore, the listing described as Ex is the one that never receives a push when alone.