It isn't ________ that I should accept such an offer as that.
A.likelyB.certainC.sureD.like在线课程A
解析：
isn't likely表示“不大可能”，likely作表语。从后面I should…as that（我竟然会）体会到使用likely妥当，而certain则表示肯定或不肯定，不宜用。sure做表语时，主体常用表示人的词。