二、when 作并列连词，引导并列分句

　　when译为“突然……或这时……”.可用在四种句式中，表示一个动作“正在发生”、“即将发生”、“刚刚完成”突然插入另一个动作。when 相当于 and just time 或and just at that time.此用法也是高考的高频考点。

　　1. was/were doing…when…正在做……这时/突然……

　　【典例】I was walking along the river when I heard a drowning boy crying for help.
　　我正沿着河边走，突然听到一个溺水儿童的呼救。
　　【高考链接】
　　（2011年浙江卷）One Friday, we were packing to leave for a weekend away my daughter heard cries for help.
　　A.after B.while C.since D.when
　　解析 此题考查连词辨析。句意为：“我们正在收拾行李准备外出过周末，这时我的女儿听到求救的呼喊。”be doing…when…表示“正在做某事，这时（突然）……”,故选D.

　　2. be about to do/be on the point of doing…when…正要做…… 这时/突然……

　　【典例】I was about to go out when an unexpected visitor came.
　　我正要出门，一位不速之客来访了。
　　She was on the point of leaving when I arrived.她正要离开，这时我来了。

　　3. had （just） done…when…刚刚做……就……

　　【典例】We had just planted 100 trees when it began to rain.
　　我们刚刚栽完100棵树，天就开始下雨了。
　　【高考链接】
　　（2009年福建卷）She had just finished her homework her mother asked her to practice playing the piano yesterday.
　　A.when B.while C.after D.since
　　解析 此题考查句型had （just） done…when…when用作并列连词相当于and at that time.句意为：“昨天她刚做完作业，这时，她妈妈就让她练习弹钢琴。”所以答案是A.

　　三、when作从属连词，引导名词性从句

　　when引导名词性从句，在从句中作时间状语，意为“什么时候”.从句常包括主语从句、宾语从句、表语从句和同位语从句。此时注意：从句要用陈述语气。
　　【典例】When we will go to Beijing hasn't been decided.我们什么时候去北京，还没有确定。
　　Please remind me when he said he was going, I may be in time to see him off.
　　提醒我他什么时候走，我好及时给他送行。
　　My question is when we will start.我的问题是，我们何时出发。
　　Tom put forward the question at the meeting when the plan can be carried out.
　　汤姆在会上提出问题：何时可以实施这个计划。
　　【高考链接】
　　（2009年安徽卷）A good friend of mine from I was born showed up at my home right before I left for Beijing.
　　A.how B.whom C.when D.which
　　解析 此题考查when引导的宾语从句。句中“when I was born”作介词from的宾语，修饰限定前面的a good friend of mine.句意为：“在我动身去北京之前，儿时的一个好友来到了我家。”答案选C.

　　以上是笔者对when作连词时的用法总结，希望对英语学习者有所帮助。