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。once a week适合用于一般体的各种时态,如一般现在时、一般过去是和一般将来时。
频率副词一般用来表示动作发生的频率,往往放在句子中间,实意动词之前,非实意动词之后;
常见频度副词按频率大小排列如下:always(100%)usually(80%)often(60%)sometimes(40%)seldom(20%)hardly(10%)rarely,never(1%)never(0%)
1.频率副词是表示与次数、频率有关的副词、如:
always(总是),usually(通常),frequently(经常),often (经常),sometimes(有时),seldom(不常),rarely(很少),never(从不),once(一次),twice(两次)等。
2.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。