<prompt> Translate the following text to EnglishKwa kuwa uhifadhi wao wa mabaki ya uwekezaji na mauzo ya bidhaa na huduma ni sehemu muhimu ya shughuli za mfuko, riba ya dhamana za mfuko inahusiana na gharama za shughuli za mfuko kama vile mapato yanayopatikana kutoka kwa kuuza bidhaa na huduma.  <response>: Since their holding of invested balances and the sale of goods and services are both integral to the funds operations, the interest on the funds securities is related to the funds cost of operations just as is the revenue earned from selling goods and services. 