when和while引導(dǎo)的時(shí)間狀語(yǔ)從句與這一時(shí)態(tài)連用.所以區(qū)別when和while的用法成了這一單元的難點(diǎn).（一）、when,while都有“當(dāng)……時(shí)候”的意思.when既可表示某一點(diǎn)時(shí)間,也可以表示某一段時(shí)間 .在when引導(dǎo)的時(shí)間狀語(yǔ)從句中,其謂語(yǔ)動(dòng)詞可以是延續(xù)性的,也可以是非延續(xù)性的,可與主句中的謂語(yǔ)動(dòng)詞同時(shí)發(fā)生,也可在其后發(fā)生.例如：1、I was just reading a book when she came into my room.她走進(jìn)我房間時(shí),我正在看書.2、Were you writing when the teacher came in?老師進(jìn)來的時(shí)候,你在寫信嗎?3、When he was a child he was always trying out new ideas.他小時(shí)候就常常試驗(yàn)一些新的設(shè)想.（二）、while只能表示某一段時(shí)間,不能表示某一點(diǎn)時(shí)間.在while引導(dǎo)的時(shí)間狀語(yǔ)從句中,其謂語(yǔ)動(dòng)詞只能是延續(xù)性的,而且也只能與主句中的謂語(yǔ)動(dòng)詞同時(shí)發(fā)生或存在.例如：1、While Jim was mending his bike,Lin Tao came to see him.正當(dāng)吉姆修自行車時(shí),林濤來看他.2、You can’t do your homework while you’re watching TV.你不能一邊看電視一邊做家庭作業(yè).（三）、另外,when和while的區(qū)別還在于：while引導(dǎo)的時(shí)間狀語(yǔ)從句多用進(jìn)行時(shí)態(tài),而when引導(dǎo)的時(shí)間狀語(yǔ)從句多用一般時(shí)態(tài).例如：1、While they were talking ,the bell rang.正在他們談話的時(shí)候,上課鈴響了.