occasion在表示：“a particular time or instance of an event（特定的）時刻；場合”時，定語從句引導詞用when；當表示：“a special or noteworthy event, ceremony, or celebration（儀式、慶典等）重大場合”時，定語從句引導詞用where。（新牛津英漢雙解大詞典）
例句：
1. In hard times, the Spring Festival was the only occasion where a family threw off the old attire and put on new clothes specially made for the festival.
2. Describe an occasion when you had to give a presentation to an audience.
例題：
D 1. Occasions are quite rare ____ I have the time to spend a day with my kids.
occasion在表示：“a particular time or instance of an event（特定的）時刻；場合”時，定語從句引導詞用when；當表示：“a special or noteworthy event, ceremony, or celebration（儀式、慶典等）重大場合”時，定語從句引導詞用where。（新牛津英漢雙解大詞典）
例句：
1. In hard times, the Spring Festival was the only occasion where a family threw off the old attire and put on new clothes specially made for the festival.
2. Describe an occasion when you had to give a presentation to an audience.
例題：
D 1. Occasions are quite rare ____ I have the time to spend a day with my kids.
A. who B. which C. why D. when 08山東