1. 副詞
   什麼時候, 何時
   當...時
   when it comes to ...(人事物)/
   when it came to ...(人事物):
   當涉及到...
   當提到...
   一談到...
   就...而論
   when it comes to ...(動詞ing ...)/
   when it came to ...(動詞ing ...):
   

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2. 連接詞
   在...的時候, 當...時
   既然, 考慮到
   然而, 雖然
   然後, 在那時
   if and when ...(完整句):
   萬一...
   當...時
   到...的時候
   

   同義字詞
   as,so long as,while
   as soon as,instantly,once
   albeit,although,altho,as,howbeit,much as,notwithstanding,though,whereas,while
   

3. 代名詞
   那時, 什麼時候
   

4. 名詞
   限定單數the when:
   (事件發生的)時間
   when the heck do/does/did ...(A: 人事物) ...(B: 動詞...)/
   (粗語)when the hell do/does/did ...(A: 人事物) ...(B: 動詞...):
   (A)到底何時做(B)?
   when the heck is/are/was/were ...(A: 人事物) ...(B: 動詞ing ...)/
   (粗語)when the hell is/are/was/were ...(A: 人事物) ...(B: 動詞ing ...):
   (A)到底何時要做(B)?
   (粗語)when the fuck do/does/did ...(A: 人事物) ...(B: 動詞 ...):
   (粗語)(A)他媽何時做(B)?
   

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例句

1. Just when you think you know.
2. When did Britain join the EEC?
3. Where and when do they happen ?
4. This is when the trouble began.
5. Your body temperature drops when you sleep.
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