Final answer:
Employee stock options improve wages only for certain employees, depending on the company's policy and the employee's role, making it the factor that improves some individuals' wages, not universally.
Step-by-step explanation:
The factor that only improves some people's wages is d) Employee stock options. Employee stock options are typically offered to employees of a company as a form of incentive which can improve their income should the company's stock perform well. This is not a uniform increase across all workers but is available only to some, usually depending on the company's policy or the employee's position within the company.
Labor unions often negotiate on behalf of all their members, which can lead to an increase for all unionized workers. Minimum wage laws legally elevate the wages for all workers that fall under the minimum wage threshold. A Universal basic income is a hypothetical scenario where all citizens would receive a regular, unconditional sum of money from the government. However, it's important to note that while stock options can provide potential wealth to employees, they can also be worth little to nothing if the company's stock does not perform well.