"连词+过去分词"作状语结构

　　
        状语从句省略后“连词+过去分词”结构的用法问题。
         状语从句用省略形式后，何种情况下可以用“连词+过去分词”结构的问题，与状语从句用省略形式位于句首或句末没关系，但与引导状语从句的“引导词”有关系。

　　
         一、一般说来，如果引导状语从句的“引导词”只用作连词而不用作介词（如once, when, while, when, though, if, unless等），它就可以后接过去分词。如：　　
Once exposed to light, the film will be damaged and get useless. 一旦曝光，胶卷就要被损坏而不能用了。　　
Although built before the war, the engine is still in perfect order. 尽管是战前制造的，这台发动机仍然处于良好状态。　　
The law could arrest the development of good research if applied prematurely. 如果草率施行，该法律将会阻滞高质量研究的进展。　　
Unless changed, this law will make life difficult for farmers. 除非加以修改，否则这条法律将给农民的生活造成困难。
When asked why he came here, the boy kept silent.当那个男孩被问到为何来这里时，他沉默不语。
When learned early on, these skills can be used throughout their college education.

         二、如果引导状语从句的“引导词”既可作连词也可用作介词（如after, before, since等），则它通常不宜后接过去分词”（因为介词后原则上不接过去分词）；若语义上需要后接过去分词，则改为“being + 过去分词”。如：　　
A tourist was robbed after being given a drugged orange. 一名旅游者在喝了一杯被动了手脚的橙汁饮料后遭到了抢劫。（摘自《柯林斯Cobuild高阶英汉双解学习词典》）　　
He scored from the penalty spot after being brought down in the box. 在罚球区内被违规撞倒后，他罚点球破门得分。（摘自《柯林斯Cobuild高阶英汉双解学习词典》）　　
The bill would be submitted for public discussion before being enacted as law. 该法案在获得通过成为法律前，将提请公众讨论。（摘自《柯林斯Cobuild高阶英汉双解学习词典》）　　
They stay here a few hours before being sent to refugee camps, which are now almost full. 他们在这儿呆了几个小时后被送往难民营，而那里现在几乎已经满员了。（摘自《柯林斯Cobuild高阶英汉双解学习词典》）　　
The wall has been like this since being damaged by a bomb. 自从被一枚炸弹炸毁之后，这堵墙就一直是这个样子。（摘自《英语语法大全》）　　
The ship had listed to one side since being struck by the speedboat. 自被快艇撞了之后，这艘船就一直往一边倾斜。（摘自《美国习语和动词短语词典》）

　　
         三、但也有个别属于特例的情况，比如 until 就是其中之一，它既可用作介词，也可用作连词，按理说不能后接过去分词，但它可以。如：　　
Leave in oven until cooked to a light brown colour. 放在烤箱里烤成焦黄色为止。（摘自《牛津英语用法指南》）　　
A man is guilty until proved innocent. 一个人只有被证明是清白后才称得上是无罪。（摘自柯林斯英语语法系列《连词》）