The investor's primary requirement is liquidity to cover tuition fees in one year. Commercial paper is a short-term, negotiable, and unsecured debt instrument, making it highly liquid and low-risk for short-term needs. In contrast, private equity securities are illiquid due to their non-public nature, and large-capitalization stocks are more volatile, making them less suitable for short-term liquidity requirements. Therefore, commercial paper is the most appropriate choice for the investor's immediate liquidity needs.