"уже" or "ещё"

"тоже" or "также"

Compound conjunction → ...то, что... / ...тот, кто...

Почему? or Зачем?

"который"

Superlative degree of adjectives

Comparative degree of adjectives

"Если..." or "Если бы..." - conditional mood

"Что" or "Чтобы"

"человек" vs "люди"

 Foreigners often ask how and when it is correct to say "человек" and "люди". It's pretty simple. "Человек" is the singular form, and "люди" is the plural form. But there are nuances (details) that you need to know.

"Потому что" or "Чтобы"

Ordinal numerals