一、悬垂结构 Dangling Element的定义
Climbing up the tower, the whole city came into our view.
正确的应该是：Climbing up the tower, we can see the whole city.
分词短语在句子中作状语时，其逻辑主语(亦称隐含主语)通常应是整个句子的主语；如果不是，而且其本身也不带自己的主语(如在独立主格结构中)，就被认为是一个语言失误。这个分词就叫做“悬垂分词”(dangling participle)或“无依附分词 ”(unattached participle)。例如：
(1) Getting down from the bus，my ankle was sprained．
（句子的主语是my ankle，但是独立成分中getting down 的逻辑主语应该是I，并不是句子的主语，所以这被认为是一个语言失误。）
(2) Driving to Chicago that night，a sudden thought struck me．
（同理，分词短语driving to Chicago that night没有带自己的主语，它的逻辑主语也不是句子的主语a sudden thought，所以也是一个语言失误。）
误：Being Sunday, they went for a picnic.
正：It being Sunday, they went for a picnic.
正：As it was Sunday, they went for a picnic.
误：To swim properly, a course of instruction was necessary.
正：To swim properly, one needs a course of instruction.
误：When a middle school student, his parents were very strict with him.
正：When he was a middle school student, his parents were very strict with him.