As, when or while?
容易混淆的單詞as, when, while?
現在的英語語法As，when和while是連詞。在某些用法中，as、when和while的含義是相同的，但它們的含義也略有不同。我們用它們來介紹從句。我們可以使用as，when和while來表示「在這段時間內」，來連接同時發生的兩個事件：
Another coach-load of people arrived as we were leaving.我們離開的時候又來了一車人。
我們經常把它們與過去連用來指代背景事件：
When the men were out working in the field, I helped with milking the cows, feeding the calves and the pigs.當男人們在田裡幹活的時候，我幫忙擠奶，餵牛犢和豬。While he was working, he often listened to music. 他工作時經常聽音樂。
我們可以在主句之前或之後加上as、when和while。當它們出現在主子句之前時，我們使用逗號：
1. As she was leaving the court, a crowd of photographers gathered around her. (before the main clause, followed by a comma)當她離開球場時，一群攝影師聚集在她周圍。（在主子句之前，後跟逗號）2. Steven was very unhappy when things weren’t going well for him.3. Lucy came into the room while he was waiting.露西在房間裡等他。
As
我們可以用as來講述兩個同時發生的事件。在as之後，我們可以使用簡單的或連續的動詞形式。進行時強調發生在另一動作進行過程中的動作：
1. As she walked to the door, she thanked them for a lovely dinner.當她走到門口時，她感謝他們做了一頓豐盛的晚餐。2. As they were signing the contract, they noticed that a page was missing.他們在籤合同時注意到少了一頁。
When
我們可以使用when來引入在較長活動或事件的中間發生的單個已完成事件。在這些情況下，我們通常在主句中使用連續動詞來描述背景事件：
He was walking back to his flat when he heard an explosion.當聽到爆炸聲時他正往公寓走。
根據上下文內容，when的意思可以是「after」或「at sample time」。
比較
While and as
我們可以用while或as來談論同時發生的兩個較長的事件或活動。我們可以使用簡單的或連續的動詞形式：
1. We spent long evenings talking in my sitting-room while he played the music he had chosen and explained his ideas.我們在我的客廳聊了很長時間，他一邊演奏音樂，一邊解釋他的想法。2. We were lying on the beach sunbathing as they were playing volleyball.他們打排球時，我們躺在沙灘上曬日光浴。
When and while
我們可以在沒有動詞的時候使用when和 while，或者沒有主語+輔助動詞be：
1. Go past the village signpost and you get to a church. When there, take the next turning right. (formal)過了村裡的路標，你就到了教堂。到那兒後，在下一個路口右轉。（正式）2. He read his book while waiting for the bus. (while he was waiting)他在等公共汽車時看書。（在他等待的時候）
備註:
as的特殊情況:
We ate our sandwiches as we walked around the park.我們邊逛公園邊吃三明治。
錯誤用法: … as walking around the park.