選 A.about to go------when
固定搭配：be about to do...when ...
所以while是絕對(duì)不可以用的
be going to do與be about to do的區(qū)別
1.be going to do:
1) 表示將要發(fā)生的事情或打算最近要進(jìn)行的動(dòng)作.如：
It is going to rain soon.快要下雨了.
2) 在含有條件狀語(yǔ)從句的主從復(fù)合句中,主句一般不用be going to,而常用will（第一人稱用shall）.如：
The football match will be put off if it rains tomorrow.如果明天下雨,足球賽將被推遲舉行.
2.be about to do:
1) 表示即將發(fā)生的動(dòng)作,在時(shí)間上指最近的將來(lái).如：
The new school year is about to begin.
新學(xué)年開學(xué)在即.
They is about to leave when they hear a siren screaming behind them.
他們正要離開時(shí),突然聽到警報(bào)器在背後尖叫起來(lái).
One day,I was about to do some shopping when he telephoned me.
一天,我正要去買東西時(shí),他打電話找我.
2) 在含有be about to do的句子中,不能再加時(shí)間狀語(yǔ).如：
Wrong:The medical team is about to start immediately.
Right:The medical team is about to start.醫(yī)療隊(duì)就要出發(fā)了.
希望能夠幫到你喲