If you are the insured's stepchild, as defined in § 404.357, we consider you dependent on him or her if you were receiving at least one-half of your support from him or her at one of these times—

(a) When you applied;

(b) When the insured died; or

(c) If the insured had a period of disability that lasted until his or her death or entitlement to disability or old-age benefits, at the beginning of the period of disability or at the time the insured became entitled to benefits.