为什么once(一次)不用加times six times(六次)就要加TIMES 为什么呢

为什么once(一次)不用加times six times(六次)就要加TIMES 为什么呢 I have beent to Beijing for three times.I have been to Shanghai for once.这两句话对么?是不是不能加for 为什么不用加for啊? 为什么用once不用ever once times a cowards die many times before their deaths,the valiant never taste of death but once.the valiant是复数,death为什么不加s? in modern times为什么加S once/twice/three times a How many times will the body of the following loop be executed?int sum = 0; int n;for (n = 9; n > 0; n = n / 2)sum = sum + n;(a) once(b) twice(c) four times(d) three times 为什么答案是三次呢?不是四次么?n=9,4,2,1各一次? how many times 和 how often..为什么once a year这个回答是用how many times问.. As (time) passes 翻译为什么不用days.times.monthss once作曾经的用法Li Yong,once a good student当中的once是曾经的意思吧?那为什么后面不用加be?应该是be a good student吧we should do something to make our class a better one.make our class a better one?这个也不用加be吗? once作曾经的用法Li Yong,once a good student当中的once是曾经的意思吧?那为什么后面不用加be?应该是be a good student吧we should do something to make our class a better one.make our class a better one?这个也不用加be吗? i will only explain it （once ）为什么explain it 后面用once而不用one 胶体为什么不用加沉淀 how many times a week?time为什么要加s? in more recent times,time为什么加s millions of times为什么time要加s 急!things of the old times.time为什么加s