1. Most of the money is spent to buy books.
2. Most of the money is used to buy books.
3. Most of the time was spent riding a bike.
4. Most of the water is spoiled.
5. Most of the playground is muddy.
6. Most of the apple was eaten by the kid.
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Are they all grammatical? Would you correct any gramatical errors? Thank you.
1 is OK, but 2 is far better.
3 is fine.
4 would be correct if you use the word "polluted" instead of "spoiled."
5 is fine.
6 is fine, but I'd make it active instead of passive: The kid ate most of the apple.