Definition: In this task, you are given a context and four options. Each option is a suggested ending for the context. You should read the context and pick the best ending for the context. Please answer with "A", "B", "C", and "D". 
Input: [header] How to use an inversion table for back pain [title] Secure your inversion table on a flat surface. [step] Ensure that all the joints, straps and pivot points are correctly connected. Do this every time you use the table in order to avoid a serious accident. <sep> (A) [substeps] Stacking your work surface will make it easier to quickly locate and properly align your free elbow joints. [title] Put a piece of paper on a flat surface. (B) [substeps] Your table should not have a flap or other covering covering your inversion table. Any flap, especially if it is rolled up or screwed up, will prevent dust from entering it. (C) [title] Assess if your patients are suffering from back issues. [step] If the sufferer of back pain frequently has a problem in their back, try to fix the issue right away. (D) [substeps] Read your inversion table instructional manual thoroughly before attempting to use the table. It will support your body weight, so it is important that all the steps are done correctly.
Output:
D