英语中的“悬垂结构”是怎么回事?

悬垂结构 Dangling Element的定义
一般在一个句子中,修饰语必须清楚地修饰句中某个词或短语,如果它不修饰句中的任何成分,而处于悬浮状态,这样的修饰语即为悬垂结构(Dangling Element).
Climbing up the tower,the whole city came into our view.
悬垂结构 的理解
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．
(2)Driving to Chicago that night,a sudden thought struck me．
由 悬垂结构 造成的错误
(1)悬垂分词
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.
(2)悬垂不定式
误：To swim properly,a course of instruction was necessary.
正：To swim properly,one needs a course of instruction.
(3)悬垂简式从句
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.
在学习语法过程中,请掌握技巧,然后理解消化.