(a) Accrued benefit requirements—(1) In general. Under section 411(b), for plan years beginning after the applicable effective date of section 411, rules are provided for the determination of the accrued benefit to which a participant is entitled under a plan. Under a defined contribution plan, a participant’s accrued benefit is the balance to the credit of the participant’s account. Under a defined benefit plan, a participant’s accrued benefit is his accrued benefit determined under the plan. A defined benefit plan is not a qualified plan unless the method provided by the plan for determining accrued benefits satisfies at least one of the alternative methods (described in paragraph (b) of this section) for determining accrued