We need 'in' to connect 'once'. This means that sometime during the three days we go to the library. We could say 'once in three days'.
My english teacher was kind enough to let me choose a song for a listening. Hello, we can say three out of eight or three eights for 3/8. Hi all, i was wondering what's the difference between three times vs times three.
We might go on day 1 or day 2 or day 3. 比如2003号房间,可以念做twenty o three,也可以念做two o o three. 121号,可以念做one two one, 也可以one twenty one。 不过一般来讲,四位数都是两位两位念,三位数两种都比. But, can we also say three over eight?