1. 母语为英语的人说成 "Time elapsed while I was sleeping.“ 的可能性要大得多!
2. 你老师的这句话有所不对.“前后(都)必须”加 ing 这一说法无根据.
while 做从属连词用,引导的时间状语从句的谓语动词是动作动词时,该动词一般用 ing 形式,铺叙主句动词所表示的动作 (如这句的 elapsed) 发生的背景 (如这句的 while I was sleeping).
以下各句子均来自同一本字典--Cambridge Advanced Learner's Dictionary (New)：
a. I read it while you were drying your hair.
b. I thought I heard him come in while we were having dinner.
下两例来自 Longman Dictionary of Contemporary English (New Edition)
a. While she read the paper, I cleaned up the kitchen. (= While she was reading the paper, ...)
b. I got malaria while travelling in Africa. (=...while I was travelling in Africa.)
3. while 做从属连词用,引导的时间状语从句的谓语动词不是动态动词时,情况见Cambridge Advanced Learner's Dictionary (New) 的例子：
a. While I was in Italy, I went to see Alessandro.
b. Tom: I'm going to the post office. Bob: While you're there can you get me some stamps?
(Tom 和 Bob 为我所加.)
4. “句中while可以用when替换么"
------可以.Time elapsed when I was sleeping. 没问题,但用 while 更好,为何要换成 when 呢!
