he was ringing up when an old man fell off his bike改成同义句.___

he was ringing up when an old man fell off his bike改成同义句.___he was ringing up when an old man

还是用 when .虽然when和while 都有“当~时候”的意思.但是 when 还有 “正在这时~,突然~”的意思,这是 while 没有的.
再问： 额？再写when 那一个句子不就两个when了吗...
再答： 其实昨天身体不认真。对不起啊。 如果真道题是这样的 __hardly__ was he ringing up when an old man fell off his bike. 这里 hardly ~~~when~~ 翻译成“一~~就~~~”。所以可以解释为： 这个男孩刚一打电话，正在这时就有一个老人从自行车上摔下来。