1. Mixture--Lettuce AND tomato
2. Mixture-- Air consists of many different elements and gasses
3. Pure-- You aren't changing the substance of wood by shaving it, but if you were thinking from a makeup level it would be a mixture to begin with
4.Mixture-- There is more than just water in pond water...bacteria and such.
5. Not sure--I might say pure but I don't know for sure
6. Mixture-- Sugar AND water
The prepositional phrase is "on a high shelf" since ON is a preposition.
Answer:
Last night, someone broke our window.
