two men had just begun to swim towards the shore,when they noticed that monster.请问句中有个when怎么解释?

问题描述:

two men had just begun to swim towards the shore,when they noticed that monster.
请问句中有个when怎么解释?

when 当。。。。时候
当他们注意那个怪兽时,两个男人就开始往岸边游了

这两个人刚朝着岸边游过去的时候他们注意到了那个怪兽

就在这时
两个男人刚开始往岸边游,就在这时他们注意到那个怪物.

那两个人正要向着岸边游去时,他们看到了那个怪物。