What is the primary characteristic of stock ownership plans within retirement plans?

The primary characteristic of stock ownership plans within retirement plans is that they typically hold more than 10% of assets in company stock. Employee stock ownership plans (ESOPs) are designed specifically to encourage employee ownership of the company's stock, which aligns the interests of employees with the financial performance of the company. By having a significant portion of assets invested in company stock, these plans aim to boost employee morale and productivity, as employees directly benefit from the company's success.

This characteristic emphasizes the importance of having a tangible stake in the company, which can foster loyalty and align individual performance with corporate success. Moreover, regulations around these plans often encourage or require a substantial investment in company stock to reap the tax benefits or to qualify as an ESOP.

While the other options mention various investment structures or restrictions, they do not accurately capture the defining feature of stock ownership plans, which is their significant allocation towards the sponsoring company's stock.