当什么时候用stb.was doing while stb.was doing

当什么时候用stb.was doing while stb.was doing 什么时候用stb.was doing while stb.was doing while I was doing可省略I was吗 while sb was/were doing与when sb was/were doing found she+doing\was doing one saturday ,i was doing my homework while what were you doing while i was away last week while+过去进行时,是不是总是sb.+was+doing sth He fell asleep while (he was) doing his homework Susan was doing the housework while her son ____the machine. I singing someone doing heard my honework while was I While I was doing my homework,the light went out.用when改同义句