Here are the correct answers for each sentence:

1. The zoo's main **B attractive** are the pandas.
2. The teacher was **B angry** with the student because he didn’t do his homework.
3. Before I set off on my journey, my father told me to drive **A safely**.
4. What’s the **A difference** between increase and decrease?
5. I hired a **A photographer** to take pictures at my wedding.
6. Despite his age, he leads an **C active** life.
7. She completed the project **C successful** and was promoted.

(Note: Sentence 7 could also accept "successfully" depending on context, but typically "successful" fits better here grammatically.)