Language points
1. Having collected and evaluated the information, I help other scientists to predict where lava from the volcano will flow next and how fast. [考点] Having collected and evaluated是动词-ing形式完成式，说明它表示动作在主要谓语表示动作之前发生。[考例1] The storm left, _____ a lot of damage to this area.    (全国卷I)A. caused                  B. to have caused  C. to cause                  D. having caused
[点拨] “暴风雨破坏”这个动作发生在left之前，故用动词-ing形式完成式。[考例2] _____ in the queue for half an hour, Tom suddenly realized that he had left his wallet at home ...