Under a Waiver of Premium rider, when does the insurer begin waiving the insured's life insurance premiums?

Why this is the answer

The Waiver of Premium rider keeps a life policy in force without premium payments when the insured becomes totally disabled. A waiting (elimination) period—most commonly six months—must elapse before the waiver applies. Once satisfied, the insurer retroactively refunds premiums paid during the waiting period and continues to waive future premiums for as long as total disability persists. Option A is wrong because temporary ailments do not trigger waiver. Option B conflates the incontestability period with the waiver mechanism. Option C imposes a hospitalization requirement that does not exist in standard waiver riders. The TX outline §II.A lists Waiver of Premium as a testable life rider.