冠词的选用Once a year,a race is held for old cars.这里为什么不是the race而是a race?每年都会有一场为旧车举行的比赛.为旧车举行的比赛,不是特定的吗?应该用定冠词the呀?我糊涂了

冠词的选用Once a year,a race is held for old cars.这里为什么不是the race而是a race?每年都会有一场为旧车举行的比赛.为旧车举行的比赛,不是特定的吗?应该用定冠词the呀?我糊涂了 Once a year的答案是什么 once a year啊,once是什么词性, 用once a year造句 once half year,twice a year 冠词a的用法 They go to the park once a year (用once a year 提问) once a year in Japan和in Japan once a year有什么区别么? They move their homes once a year.划线提问,划once a year.对不起,刚开号, once a year,a race is held for old cars.这里的 is held 是怎么回事? ''I once a year have a party.''对吗?豆腐干活佛； a one-year-old son为什么冠词是a不是an ?急求!one的o不是原因字母么？ We have a party once a year.（就划线部分提问,划线部分是:once a year) Everyone has one and they only have it once a year的答案 you must clean your watch once a year的同义句改为被动语态， you must clean your watch once a year,的句子成分咋画 I like to go travelingA.one time the year B.once a year C.one time in a year D.once in a year We do a bird count once a year.(对画线部分提问)划线部分是once