once a week是频率副词,表示的是一种不断重复的行为频度,往往放在句子中间，实义动词之前，非实义动词之后，在否定句中，有的频度副词位于否定词之前或之后均可，而有的频度副词则必须位于否定词之后，还有的频度副词却必须要位于否定词之前。
once a week是频率副词吗频率副词等级
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、频率副词用在be动词后
He was always late.他以前经常迟到。
4、频率副词用在实意动词前
My father usually walks home.我的父亲经常步行回家。
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.
