The employees of Ace Trucking Company must each pay a portion of the premium for their group insurance. This means they are members of a

A noncontributory group plan is one where the employer pays the entire premium, and employees do not contribute financially. Since the question specifies that employees pay a portion of the premium, this option is not applicable.

A participating plan generally refers to insurance policies that allow policyholders to receive dividends or share in the profits of the insurance company. While this type of plan can involve both employer and employee contributions, it does not specifically imply that employees must pay a portion of the premiums, making it an incorrect choice.

A nonparticipating plan does not allow policyholders to share in dividends or profits of the insurance company. Similar to the noncontributory plan, this option does not indicate any requirement for employee contributions, thus making it irrelevant to the context of the question.