Here are the completed sentences with suitable connectors:

1. I am going shopping. It rains, **however**.
2. I have studied hard for the exam. I **failed**.
3. **Although** Aylin knew the post office's address, he didn't tell me.
4. Hakan drank two cups of coffee **though** he drank a cup of coffee before.
5. Sevgi went to school **although** she was ill.
6. **Although** the exam is so difficult, I had a good mark.
7. I missed the bus. **Nevertheless**, I wasn't late for school.
8. We don't like camping. We, **however**, love fishing.
9. We still fed the cat **although** it wasn't hungry.
10. He decided to buy that car **although** it was so expensive.
11. **Although** he is 30 already, he doesn't want to work to earn money.
12. I don't know how to play chess. I really want to learn it, **though**.
13. **Nevertheless**, it was late, we still went out for a while.
14. **Although** we didn't have much money, we went shopping very often.
15. We managed to do it **although** he is absent from work.

Feel free to ask if you need any further assistance!