In the United States, money market funds can be divided into three categories according to the level of risk. 　　 In the United States, money market funds can be divided into three categories according to the level of risk. 　　 1, Treasury bill money market funds, which invest mainly in treasury bills, marketable securities guaranteed by the government, etc. These securities generally have a maturity of less than one year, with an average maturity of 120 days. 　　 2,Diversified money market funds, which are commonly referred to as money market funds, usually invest in a variety of marketable securities such as commercial paper, treasury bills, securities issued by U.S. government agencies, negotiable certificates of deposit, bankers' acceptances, etc., which have similar maturities as the aforementioned funds. 　　 3, Tax-exempt money funds, which are used primarily for short-term financing of high-quality municipal securities, also include municipal medium-term bonds and municipal long-ter