凡是由lest（以免；免得）,in case（以防）和 for fear that（生怕,唯恐）引导的目的状语从句中,用“should+动词原形 其谓语部分should可以省略.例如：
Keep quiet in case you（should）interrupt him
when he is busy．要保持安静,以防打扰他.
She is now studying for fear that she（should）fail in
English．她现在很勤 奋,生怕英语不及格.
You must wake him early lest he（should）be late for
school．你务必早点叫 醒他,以免他上学迟到.
三个都能省的.