Final answer:
An increased number of workers will cause the supply curve to shift to the right in the PPF. More educated workers can also lead to increased productivity and an outward shift in the PPF.
Step-by-step explanation:
An increased number of workers will cause the supply curve to shift to the right in the production possibilities frontier (PPF). This is because more workers mean more available resources, which can lead to increased production and output. For example, if a country experienced population growth or immigration, it would have more workers available, thereby expanding its PPF.
On the other hand, options A, B, and D would not directly lead to an outward shift in the PPF. Less workers (option A) would result in a decrease in available resources, potentially leading to a contraction in the PPF. Computers with new abilities (option B) may increase productivity, but without an increase in the number of workers, the PPF would not shift outward. Option D, none of the above, is incorrect because an increased number of workers can lead to an outward shift in the PPF.
Therefore, the correct answer is C. more educated workers, as an increase in the education level of workers can also lead to increased productivity and an outward shift in the PPF.