Using formal language both in oral and written form is an advantage for you. You will be noticed by people and they will remember you more because your language stands out from the language use of others.
Using formal language infers that you are a well-educated and well-round person. People will likely believe in what you say because it will give credence to you and your abilities.
However, when you use formal language with people who are not as well verse to its usage, you will face discrimination or ill-will because they will feel insecure and intimidated by you.
The answer to your question is C
1. производительность труда
2. удовлетворённости жизнью
3. благосостояние населения
4. население страны
5. наличие еды
6. приобретение автомобиля
7. плитка шоколада
8. прилив силы
9. уровень счастья
10. отсутствие друзей
11. тысяча долларов
12. смысл жизни
13. рост благосостояния
