- 1 decade agoFavorite Answer
while --- 用既時候，果句句子既tense應該系be (v + ing )
eg. While Mother was watching TV, the bell rang.
when --- 幾時都用得… 咩tense 都可以，besides be (v +ing )
eg. When she arrived, the boy was killed.
As --- 當；講緊果兩件事吾一定要同時進行緊，適用於時間更長既~
eg. Mary was busy as she didn't have time to write to her penfriend.
- 1 decade ago
--even though; although: While she appreciated the honor, she could not accept the position.
--at the same time that (showing an analogous or corresponding action): The floor was strewn with books, while magazines covered the tables.
--at what time: to know when to be silent.
--at the time or in the event that: when we were young; when the noise stops.
--at any time; whenever: He is impatient when he is kept waiting.
--(used correlatively after an adjective or adverb prec. by an adverbial phrase, the adverbial as, or another adverb) to such a degree or extent that: It came out the same way as it did before. You are as good as you think you areSource(s): www.dictionary.com