1、To be doing" 是一种常见的结构，意思是正在做某事。它是 "be" 的原形动词（如 "am," "is," "are"）加上 "doing" 的现在分词形式。例句：I'm studying for a test right now. (我正在复习考试)They are having a barbecue in the backyard. (他们正在后院烧烤)
2、注意，"to be doing" 可以用来表示一段时间内的持续性动作。例句：I've been working on this project for weeks. (我已经做这个项目几周了)She's been practicing the piano for hours. (她已经弹钢琴几个小时了)中文翻译：正在做某事。
