Rewrite each of the following sentences, changing the subject of the verb to the singular, inserting a or an before the subject, as appropriate, and changing the verb to agree with the subject. For example:
Violins are difficult to play.
A violin is difficult to play.
Unions have been formed.
A union has been formed.
Answers are always provided.
An answer is always provided.
Heirs have many friends.
An heir has many friends.
1. Avocados are expensive.
2. Windows are an important feature of an artist's studio.
3. Umbrellas should not be used during a thunderstorm.
4. Horses can be useful in the mountains.
5. Cashews are a type of nut.
6. Onions can be used for flavoring soup.
7. Trucks have many uses.
8. Hours passed.
9. Sentences should have proper punctuation.
10. Escalators are very convenient.
11. Uniforms must be worn.
12. Boxes were found on the floor.
13. Marshes lie beyond the city boundary.
14. Ideas can be valuable.
15. Eggs are a good source of protein.
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