What statement pertaining to defined contribution registered pension plans is true?

a$)$ When an employee joins the plan, the exact pension benefit payable at retirement is known.

b$)$ Plan members have the opportunity to purchase past service benefits after two years of membership in the defined contribution plan.

c$)$ The maximum employer$/$employee contribution is limited to the lesser of $18\%$ of the employee's earnings and the annual money purchase contribution limit$.$

d$)$ Defined contribution plans can include inflation$-$protection provisions