貌似没有说完整,把整个句子都放上来啊孩纸不是句子啊，只是通过这个while walking the dog you werecaless........这句话总结的！只是我不明白系动词（非主语），是什么意思？这样啊，懂了!就是可以省略非主句主语的系动词！就是说从句里的主语和系动词同时被省去哦~比如当过马路的时候，你应该小心。when you are crossing the road, you should be careful.when crossing the road, you should be careful.