這句話是不是有些拼寫錯(cuò)誤?They(不是tehy) eat beef once or(不是of) twice a week.中文意思：他們每周吃一到兩次牛肉.
once or twice是頻度副詞做狀語(yǔ),對(duì)該狀語(yǔ)提問,用How often,意為：多久一次.
所以特殊疑問句如下：
How often do they eat beef?
如果硬要對(duì)括號(hào)內(nèi)詞提問,則：
How often do they eat beef in a week?
這里的介詞in是必須的,為避免引起歧義.