Ex. 1 Вставьте предлоги on, in, at 1. His office is the top of the stairs.
2. I spent this weekend a small village the mountains.
3. Jane bought a three-room flat the third floor.
4. Let's meet the exit to the Supermarket.
5. She met the shop the beginning of Central Park.
6. There are a lot of shops the end of the street.
7. There's somebody the door.
8. You are the only one the world who knows it!

1. His office is on the top of the stairs.
In this sentence, we use the preposition "on" to indicate the location of his office. It means that his office is situated physically on the top of the stairs.

2. I spent this weekend in a small village in the mountains.
Here, we use the preposition "in" to show that the person spent the weekend inside a small village located in the mountains. The preposition "in" is used to indicate being inside a place.

3. Jane bought a three-room flat on the third floor.
In this sentence, we use the preposition "on" to indicate the location of the flat. The flat is physically positioned on the third floor.

4. Let's meet at the exit to the Supermarket.
Here, we use the preposition "at" to specify the place where the meeting will take place. The meeting is planned to happen at the exit of the Supermarket.

5. She met the shop at the beginning of Central Park.
In this sentence, we use the preposition "at" to indicate the specific position where the shop is located. The shop is situated at the starting point or entrance of Central Park.

6. There are a lot of shops at the end of the street.
Here, we use the preposition "at" to specify the particular position of the shops. The shops are located at the conclusion or farthest point of the street.

7. There's somebody at the door.
In this sentence, we use the preposition "at" to indicate the location of the person. The person is standing near or in front of the door.

8. You are the only one in the world who knows it!
Here, we use the preposition "in" to emphasize the person's unique position or state. The person is considered to be in an exclusive or special position of being the only one who knows something in the entire world.