1. The key to ______ the problem is to meet the demands ______ by the customers.
A. solving; making B. solving; made C. solve; making D. solve; made
2. One of the meteor (陨石) pieces was found to have crashed into a frozen lake, ______ a six-meter wide hole.
A. left B. leaving C. to leave D. having left
3. Scientists have warned that coral reefs are likely to become the world’s first ecosystem ______ because of global warming.
A. to disappear B. disappearing C. disappeared D. having disappeared
