if （it is） necessary是什么现象,假设都可以省略?

if （it is） necessary是什么现象,假设都可以省略? Fill in the blanks where( it is ) necessary 为何可以省略括号里的 if it is necessary /if necessary /when it is necessary 意思一样吗 when it is necessary 为什么可以变为when necessary? 英语翻译Similarly,it is necessary to determine if these effects it is necessary . If it is necessary,please write to your parents.改为if条件状语从句 It seems that/as if在什么时候可以省略 Is it necessary and if so,what should be included?求前半句英文的中文翻 it is necessary that a person do exercises every day if he w 'it is believed that +从句' 中that可以省略吗? it is said that 可以省略that吗