[] having an official position在职的；现任的◆the incumbent manager/chief executive在职经理／行政总裁 [] having a large market share有很大市场份额的◆incumbent operators without a real threat of competition没有真正竞争威胁的主导运营商 () [] necessary as part of sb's duties有责任的；义不容辞的；必须履行的◆It was incumbent on/upon them to attend.他们必须出席。