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.