be doing 後面加when或 while都可,試看例句兩個:Mum was cooking while Dad was watching TV. (媽媽在做飯,爸爸在看電視,表示兩個動作同時發生)。
He was crossing the road when his phone suddenly rang. (他手機響的時候正在過馬路)。兩個例句,was doing後面不同的情況。
作爲時間狀語從句的連詞when和while都可以解釋爲“當…的時候”,它們的區別是while的後面必須使用進行時態be doing,而when後面既可以使用一般時態也可以使用進行時態。
至於這兩個連詞前面是用進行時態還是一般時態則沒有太大的講究。
be doing+when意思是:正在做某事,這時……例句,He was driving on the street when another car crashed into his car.