1. 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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2. Fill in each blank with either the indefinite article (a or an) or the definite article (the). Use a or an with nouns referring to people or things which have not been mentioned previously, and use the with nouns referring to people or things which have been mentioned previously.

I had never visited Seretnay Park before. Last week I went to ____ park and chose ____ tour to take. There were twenty tourists and one guide. ____ guide asked what we wanted to see. I said I had never seen ____ eagle, and I would like to see one. ____ child on ____ tour said he would like to see ____ beaver, since he had heard there were many in ____ park. ____ guide said he would do his best. First he led us along ____ road, and then we turned off onto ____ path. To our right was ____ marshy pond.

Suddenly ____ child who had spoken before shouted, "Look! I see ____ beaver!" Of course ____ beaver was startled. It slapped its tail and disappeared into pond.

Our guide pointed to ____ pile of sticks and said, "That's where ____ beaver lives. That's his house." I had my camera with me, and took ____ photograph of ____ house.

As we were standing there, ____ guide was looking across ____ pond through ____ small telescope. After a minute, he tapped my shoulder and handed me ____ telescope. He pointed to ____ tall tree and said, "Do you see that white speck? That's ____ bald eagle."

I had difficulty focusing ____ telescope, but finally I saw ____ eagle. As I watched, ____ eagle spread its wings and soared over the water.

It was ____ wonderful experience for me to see some of the wild creatures that live in ____ park.
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3. Fill in each blank with a, an or the. Be prepared to justify your choice. For example:
      ___ moon is full tonight.
      The moon is full tonight.

      He is ___ singer.
      He is a singer.

      Please sit in ___ center of the boat.
      Please sit in the center of the boat.

      The room costs twenty dollars ___ day.
      The room costs twenty dollars a day.

      ___ wheel is considered one of mankind's most important inventions.
      The wheel is considered one of mankind's most important inventions.

1. His aunt is ____ teacher.
2. ____ architect is trained in design, drafting, and economics.
3. ____ ostrich is the world's largest bird.
4. Buses pass this point two or three times ____ hour.
5. Plants gain energy from the light of ____ sun.
6. I woke up in ____ middle of the night.
7. She is ____ doctor.
8. ____ seal is an excellent swimmer.
9. Our eyes usually blink several times ____ minute.
10. At ____ equator, sunrise occurs at the same time each day.
11. He is ____ author.
12. They wanted to hear ____ end of the story.
13. Such a severe storm occurs only once ____ decade.
14. Mount Everest is tallest mountain in ____ world.
15. There is an index at ____ back of the book.
Answers
 

Answers to Exercise 1:
1. An avocado is 2. A window is 3. An umbrella should not be used 4. A horse can be 5. A cashew is 6. An onion can be used 7. A truck has 8. An hour passed 9. A sentence should have 10. An escalator is 11. A uniform must be worn 12. A box was found 13. A marsh lies 14. An idea can be 15. An egg is

Answers to Exercise 2:
the park, a tour. The guide. an eagle. A child, the tour, a beaver, the park. The guide. a road, a path, a marshy pond. the child, a beaver. the beaver. the pond. a pile, the beaver. a photograph, the house. the guide, the pond, a small telescope. the telescope. a tall tree. a bald eagle. the telescope, the eagle. the eagle. a wonderful experience, the park.

Answers to Exercise 3:
1. a [profession] 2. An [general statement] 3. The [considered as a class] 4. an [per] 5. the [obvious what is meant] 6. the [unique] 7. a [profession] 8. A [general statement] 9. a [per] 10. the [unique] 11. an [profession] 12. the [unique] 13. a [per] 14. the [unique], the [obvious what is meant] 15. the [unique]