首先请看2002年春季高考试题第27小题：
This is Ted's photo. We miss him a lot .He _______trying to save a child in the earthquake.
A. killed B.is killed C.was killed D.was killing
简析：由于空格后是个分词结构，造成这道题目有很大的迷惑性。如果懂得了动名词trying…前省略了介词in ，就会发现这道题目只是一道简单的考查被动语态的题目，从而可以选出C项。
这个知识点出现在高三英语课本上册第22课：
Second ,much energy is wasted producing things that are thrown away.其次，浪费了大量的能源去生产那些要扔掉的东西。
类似的句子还有：
A lot of difficulties may be met building the bridge across the river.
在这条河上建筑桥梁可能会遇到很多困难。
其实，像这种省略in 的句子结构，高中阶段我们也见过不少，本文特作如下归纳：
1，have some difficulty/trouble (in)doing sth.做某事有困难/麻烦
1)I have much difficulty (in)understanding what you say .
我很难听懂你的话.
2) He had no trouble/difficulty (in)repairing my TV.
他毫不费力地修好了我的电视。
2，spend time/money…(in)doing sth.花时间/金钱……做某事
1)He spent his life (in) writing the book.
他花了一生的时间写这本书。
2)They spent a lot of money (in) advertising their new products.
他们花了很多钱为他们的新产品做广告。
3,There/It is no good /use/ help …(in) doing sth .做某事没好处/用处/帮助……
1〕There is no good (in)discussing it any further now.
现在再继续讨论这件事也没用。
2〕 It is no use (in) trying to explain it to her clearly.
想向他解释清楚这件事是徒劳的。
4，have a good /pleasant /hard…time (in) doing sth.做某事愉快/高兴/艰难……
1)I had a hard time (in) carrying out this task.
我非常艰辛地完成了这个任务。
2〕 They had a pleasant time (in) chatting with each other.
他们互相聊得非常愉快。
5，be busy (in) doing sth.忙于做某事
1) We are busying (in) making preparations for the end-of-term exams.
我们在忙于准备期末考试。
2) The peasants are busy (in) getting crops.
农民们在忙于收割庄稼。
参考资料：http://blog.sina.com.cn/s/blog_5c4bbd610100arsx.html