状语从句与非谓语相互转化
1．Since he was defeated, he left the room sadly.
1.Defeated, he left the room sadly.
  2. Once he had been appointed supreme    commander, he took the stern measures    expected of him.
2.(Once) appointed supreme commander, he took the stern measures expected of him
3. The stranger, after he had discarded his jacket, moved threateningly towards me.
3.The stranger, having discarded his jacket, moved threateningly towards me.
4. He wrote his greatest novel while he       was workin ...