两个都行的...但turn it on/off比较常用,我个人比较偏向.很少听人说turn on it,但如果是实际的物品就刚好相反,像 turn on/off the radio,没人倒过来说的 how to do it 怎么做 when to do it 没有这说法,或者不常用 应该 when will we do it/ when are we going to do it what to do it 语法错误...应该what to do with it 用它来干嘛 why to do it 没有这说法 应该 why are we doing it/ why did we do it