根据句意和所给汉语的意思，完成句子，每空一词。
1. Birds are the natural ______（敌人）of many insects.
2. When they heard that Martin Luther was killed,they were _____（彻底）shocked.
3. Do you lie______（醒着）at night,worrying about things?
4. Almost three _____（四分之一）of the earth’s surface is covered by water.
5. We believe that we can achieve very good exam results______（通过）great effort.