Explanation:

- Efficient utilization of inputs: With well-trained and skilled workers, resources and inputs can be used more effectively, reducing waste and increasing productivity. This aligns with human capital enhancement.

- Increase in the stock of physical capital: While human capital can support the effective use of physical capital, it doesn't directly increase its stock. Physical capital refers to tangible assets like machinery and buildings.

- Increase in GDP Growth: A well-educated and skilled workforce drives innovation and productivity, leading to economic growth. This is a direct benefit of human capital formation.

- Both a) and c): Combining efficient resource utilization and contributing to GDP growth, human capital formation impacts both these areas positively.