大家好,我在文法书上面看到一段文章,有点小小的疑问想请教,文章如下 Stella was alone in a strange city.She walked down the avenue slowly,looking i n shop windows.Suddenly,she turned her head and looked behind her.Someone had called her name. 以上文章的文法时空背景应该是设定在过去的时间,但是为什么look会是ing的形式呢? 恳请神人不吝赐教,谢谢