Adjectives with fixed prepositions

You already know that there are adjectives and nouns, as well as verbs, that take a fixed preposition. Just like with verbs, you have to learn the combinations of adjective and preposition. A few adjectives with fixed prepositions that you already know include:

traurig + über + accusative
Ich bin traurig über den Streit.

wütend + auf + accusative
Yara ist wütend auf ihren Nachbarn.

If you have argued with someone or got mad with someone, you can use the adjective sauer:
sauer + auf + Accusative
Nico ist sauer auf seinen Bruder.

If you want to ask about the noun that is connected to a preposition, you have to use the preposition in the question. With questions about people, the preposition always comes before the question word:

Auf wen ist Nico sauer? – Auf seinen Bruder.

In colloquial language, if you are asking about things, you would often form the question with the preposition + was. 

Über was bist du traurig? – Über den Streit.