介词填空。
1. They are used _____ seeing in the dark.
2. They were invented _____ 1863.
3. George wanted _____ make the customer happy.
4. Potato chips were invented _____ a chef called George Crum.
5. He was boiling drinking water _____ an open fire.
6. Some leaves _____ a nearby bush fell _____ the water and remained there for some time.
7. This beverage was discovered _____ three thousand years before that.
