Special vesting rules apply to qualified defined contribution plans with voluntary employee contributions and matching employer contributions. Which of the following statements is $($are$)$ true with respect to these vesting rules?

I.Employer contributions must vest immediately.

II$.$Graded vesting is permitted, and employer contributions must be $20$ percent vested after $2$ years, with an additional $20$ percent vested in each of the next $4$ years.

Group of answer choices

I only

II only

both I and II

neither I nor II