Once a year,a race is held for old cars.是个什么结构?

once a year,a race is held for old cars.这里的 is held 是怎么回事? Once a year,a race is held for old cars.这里为什么不是By 而是for? Once a year,a race is held for old cars.是个什么结构? 新概念英语2册56课once a year,a race is held for old cars. old car race is held ones a year. 请帮我分析下句子结构,关键是once a year 新概念英语2册56课问题1.once a year,a race is held for old cars.请问能否把a去掉改成：once a year,race is held for old cars.为什么?2.old car race is held ones a year.请问能否加个an改成：an old car race is held ones a year ''I once a year have a party.''对吗?豆腐干活佛； i visit the great wall once a year翻译 once a year啊,once是什么词性, 用once a year造句 once half year,twice a year I like to go travelingA.one time the year B.once a year C.one time in a year D.once in a year I ___(write) a letter to Peter once a week last year. Once a year的答案是什么 I can ______you in a race 关于定冠词和不定冠词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? 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 I go to see my grandparents (once) a year.(对括号部分提问） 英语翻译请翻译 we visited it once a year with the school class I was in.