概念引入
在初中和高一，我们已经学过动词-ing形式的用法，而在学习过去分词的过程中，也穿插着与动词-ing形式的用法的区别，那么在本单元我们就把学过的有关动词-ing形式的内容复习并小结一下。
看下面句子：
1. Having collected and evaluated the information, I help other scientists to predict where lava from the volcano will flow next and how fast.
2. I was appointed as a volcanologist working for the Hawaiian Volcano Observatory twenty years ago.
3. My job is collecting information for a database about Mount Kilauea, which is one of the most active volcanoes in Hawaii.
