once a week是頻率副詞,表示的是壹種不斷重復的行為頻度,往往放在句子中間，實義動詞之前，非實義動詞之後，在否定句中，有的頻度副詞位於否定詞之前或之後均可，而有的頻度副詞則必須位於否定詞之後，還有的頻度副詞卻必須要位於否定詞之前。
once a week是頻率副詞嗎
頻率副詞等級
all the time 100%；
almost，always 90%；
generally，usually 80%；
often，frequently 60-70%；
as often as not 40-50%；
sometimes，at times 20-30%；
occasionally，from time to time 10%；
hardly，seldom，rarely 5%；
never 0%。
3、頻率副詞用在be動詞後
He was always late.他以前經常遲到。
4、頻率副詞用在實意動詞前
My father usually walks home.我的父親經常步行回家。
once a week造句1、How many skateboard classes once a week?
2、Occurring, appearing, or done once a week or every week.
3、Go once a week if you can.
4、Lung cells were replaced once a week.
5、She does the aerobics once a week.
6、What you should do: Run Yasso 800s once a week.
7、We used go to the movies about once a week.
8、Hence clean the ears once a week with cotton buds.
9、They also check for diseases or pests once a week.
10、Proofread the English Ad once a week by Email.