1, What I saw astonished me
→ I was astonished at what I saw.
2, Before going out with him, I had finished the homework.
→ When I had finished the homework, I went out with him.
3, He usually drinks coffee in the morning.
→ He is used to drinking coffee in the morning.
4, It took us forty minutes to fly from Hue to Ho Chi Minh City.
→ The flight lasted forty minutes from Hue to Ho Chi Minh City.
5, I felt tired because of a sleepless night.
→ A sleepless night made me feel tired.