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 flex your back [title] Do abdominal exercises. [step] Abdominal exercises will flex you back each time you roll your body forward or to the side. Include a few abdominal exercises in your regular exercise routine. <sep> (A) Try the following combinations : [substeps] Stretch at least three times a day. This will increase your flexibility and prevent injuries. (B) Specific physical exercises that target specific muscle groups should not be attempted on surfaces with specific target areas. [substeps] Swimming and swinging your arms forward and to the side should be two examples of abdominal exercise. (C) [substeps] To do these exercises, sit in a comfortable position. Slide your lower back back forward as far as it will go, hold for 30 seconds, then slowly lower your back. (D) There are lots of different abdominal exercises you can try including : [substeps] Sit ups crunches oblique crunches do bicycle crunches | bicycle crunches] ] [title] Try supermans. [step] Lay down on your stomach with your arms straight out in front of you and your legs straight out behind you.
Output:
D