An expense ratio is OA. the ratio of a mutual fund's assets to its managing and/or operating costs. OB. an annual fee charged to investors by mutual funds to defray their managing and/or operating costs. OC. an annual fee paid by mutual funds to government to maintain all licenses and certifications. OD. the proportion of a mutual fund's assets that must be liquidated annually to cover its managing and/or operating costs. Expense ratios affect the value of an investor's portfolio by