Regulation 12 CFR 9.10 indicates that cash can be invested:

Regulation 12 CFR 9.10 outlines the investment of cash by fiduciaries and specifies the expectation for the timely investment of cash. The correct answer highlights that "promptly" refers to the practice of investing cash on a daily basis for most institutions. This is important as it emphasizes the role of fiduciaries in ensuring that client funds are invested efficiently to maximize returns and minimize idle cash, which could lead to lost opportunities for earning income.

Investing cash promptly is crucial in financial management, especially considering the dynamic nature of financial markets. By interpreting "promptly" to mean a daily investment routine, institutions can align with regulatory expectations and provide better service to their clients by optimizing cash usage. Therefore, this answer accurately reflects the intent and requirements set forth in the regulation regarding the management of cash for fiduciary responsibilities.