余伟民的回答：

原发布者:张_景瑞 occasion的用法1.[C]particulartime(atwhichaneventtakesplace)（事情发生的）时刻，时候，场合onthis/thatoccasion此时/彼时onthepresentoccasion在这次ononeoccasion=once有一次onrareoccasions偶尔I’vemethimonseveraloccasions.我见过他几次。Iwasnotathomeonthatoccasion.那时我正好不在家。Ionlywearatieonspecialoccasions.我只在特殊场合才打领带。Ononeoccasionheevenrangmeinthemiddleofthenight.有一次他甚至在午夜给我打电话。Onthisoccasion,asithappens,theenginestartedimmediately.2.suitabletimeforsth.;opportunity时机；机会Youshouldgothereiftheoccasionarises.如果有机会，你应当到那里去。Heusedtheoccasiontoexpresshisgratitude.他利用那机会表达了感激之情。3.[C]specialeventorcelebration特殊的事件或庆典Theweddingwasquiteanoccasion.该婚礼是一盛会。4.[U]原因；理由；需要I’vehadnooccasiontovisithimrecently.我最近无需去看他。Youhavenooccasiontobeangry.你没有理由生气。Therewasnooccasiontobesorude.没有理由这样粗鲁。5.习语asenseofoccasion场合意识onoccasion(s)偶尔；必要时ontheoccasionofherdaughter’swedding在她女儿的婚礼上e.g.Heworeshabbiestclothes

刘木子的回答：

occasion 英 [??ke??n] 美 [??ke??n] n.场合;机会，时机;理由;需要 vt.惹起，引起 by occasion of：因为 on occasion：某个场合