when與while都可以.
while與when經(jīng)常被用在含有一般過(guò)去時(shí)及過(guò)去進(jìn)行時(shí)的句子中.在這種情況,短的動(dòng)作可以在長(zhǎng)的動(dòng)作過(guò)程中發(fā)生,即：長(zhǎng)的動(dòng)作發(fā)生在短動(dòng)作前.while一般指相對(duì)長(zhǎng)的動(dòng)作；when即可以指相對(duì)長(zhǎng)的動(dòng)作也可以是指相對(duì)短的動(dòng)作.在所給句子‘fell down’相對(duì)‘running’是短動(dòng)作,因此,在這個(gè)句子里,‘when’ ‘while’都可以用.
通過(guò)以下句子也許可以進(jìn)一步理
While he fell down,he was running 錯(cuò),因?yàn)閣hile只能指相對(duì)長(zhǎng)動(dòng)作
when he fell down,he was running 對(duì),因?yàn)閣hen 可指長(zhǎng)或短動(dòng)作
He fell down,when he was running 對(duì),因?yàn)閣hen 可指長(zhǎng)或短動(dòng)作
He fell down,while he was running 對(duì),因?yàn)閣hile 指相對(duì)長(zhǎng)動(dòng)作