求救！咋樣，可以成攻救人？
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4 people need to cross a bridge before it collapese,  they have seventeen minutues befor the collapse. there is only one flashlight and each must have the light to cross. the bridge can only hold 2 people at a time ,can you save them ？ 1. 1 old man （need 10 minute to cross） 2. 40  year old woman （need 5 minute to cross） 3. 20 year old （need 2 minute to cross）