<prompt> Translate the following text to EnglishNi vigumu kuamua tarehe za sherehe mbalimbali kwa usahihi, kwa kuwa nyingi zinategemea kalenda za mwezi ambazo hutofautiana kila mwaka.  <response>: It is difficult to fix precisely the dates of the various festivals, as most of them are determined by lunar calendars which vary from year to year. 