Teorija

Study the information about ‘must’ .
  
Must

1. To express obligation or duty.
 
This also refers to laws and regulations.
 
You must wear a seatbelt at all times.
  
car-1865856_640.png
Рис. \(1\). Seatbelt  
 
2. To emphasize the necessity of something.
 
You must study hard before the test.
You must drive carefully.
  
3. Deduction - sure that something is true (Certainty).
  
We use this when we don't know but we are certain that it is true (based on evidence).
 
Dinosaurs were huge, they must have eaten a lot.
  
dinosaur-958011_640.jpg
Рис. \(2\). Dinosaur  
 
4. Expresses positive logical assumptions (Must + have + past participle).

He must have won the lottery with the new house and car he has just bought.
  
balls-6077901_640.jpg
Рис. \(3\). Lottery  
 
5. A strong recommendation.
  
Something that is highly recommended (stronger than using should)
 
The ice cream is delicious. You must try some.
  
ice-3611698_640.jpg
Рис. \(4\). Ice cream

Mustn't

The negative is mustn't which refers to prohibition (negative obligation)
 
Mustn't = Must not
  
You mustn't use your mobile phone while you are driving.
  
steering-wheel-801994_640.jpg
Рис. \(5\). Steering wheel
Atsauce:
Рис. 1. Seatbelt, 2016, https://pixabay.com/images/id-1865856/ Pixabay License CC0 Free for commercial use No attribution required
Рис. 2. Dinosaur, 2015, https://pixabay.com/ru/photos/динозавр-гад-млекопитающее-дино-958011/ Pixabay License CC0 Free for commercial use No attribution required
Рис. 3. Lottery, 2021, https://pixabay.com/ru/photos/шарики-розыгрыш-призов-лотерея-6077901/ Pixabay License CC0 Free for commercial use No attribution required
Рис. 4. Ice cream, 2018, https://pixabay.com/ru/photos/льда-мороженое-3611698/ Pixabay License CC0 Free for commercial use No attribution required
Рис. 5. Steering wheel, 2015, https://pixabay.com/ru/photos/рулевое-колесо-автомобиль-801994/ Pixabay License CC0 Free for commercial use No attribution required