You will be given a definition of a task first, then some input of the task.
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".

[header] How to stop a severe headache after a long run [title] Recognize the symptoms. [step] Primary exercise headaches are the most common type of exercise headache. It is not known why some people experience primary exercise headaches, although some doctors believe it may have something to do with dilated blood vessels caused by strenuous activity. <sep> (A) [substeps] Primary exercise headaches occur in children who exercise too much, too quickly and quickly. They start soon after a strenuous activity (such as running), and become harder or harder the following season. (B) Common symptoms of primary exercise headaches include : [substeps] A throbbing pain in one or both sides of the head. Headaches that begin during or immediately after strenuous activity. (C) The risk of secondary exercises being both painful and autoimmune is great. In some patients, their primary exercise headache is itchiness or inflammation of the exocrine glands in the part of their neck, eye, and spine. (D) They may manifest themselves in proexcavation, swelling, and discomfort. [substeps] Secondary exercise headaches usually occur after exercise and they tend to be more frequent in people who have had some strenuous activity.
Output:
B