Answer:
2. auf den
3. mit denen ich gespielt habe
4. mit denen ich lerne
5. bei dem Anna kauft
6. von dem sie das Haus gekauft hat.
7. an die du denkst
8. an der ich mich geärgert habe.
Step-by-step explanation:
2. "Bus" is a masculine word in German therefore it is "den".
3. "kinder" is plural so it is "denen".
4. "bücher" is also plural.
5. "der (den) bäcker" is masculine but it's in 3rd person so it is "dem".
6. same as nr. 5
7. "die" plural but it is an exception, it is die instead of denen.
8. in this case die is not for plural but for feminine, however in the answer this is changed to masculine because the feminine is already used in the sentence before the comma.