A

　　Thepartbeforethecommacanbeconsideredasacompletesentence,sothepartafterthecommacanonlybeconsideredasanattributiveclausetomodifythepreviouspart.Thus,youcanonlychoosefromtheword"which"and"that".Consideringthereisapreposition"of"beforethelead-inword,youcanonlychooseAastheanswer.