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
问题描述：
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
答