once用作连词时,意为“一旦……就……”,用于连接时间状语从句,相当于as soon as.如：
Once you start,you will never give up.一旦你开始了,你就不要放弃.
Once you begin to read it,you will like it.一旦你开始读,你就会喜欢它.
Physics is easy to learn once you understand the rules.一旦你理解了规则,物理就不难学了.
注意：once引导的是时间状语从句,从句要用一般现在时代替将来时.