Sure! Here are suitable conjunctions to complete the sentences:

1. My father wants me to become a doctor, **but** I want to become a designer.
2. It is a challenging task, **so** it takes me a lot of time to do it.
3. Should I stay in and watch TV **or** should I hang out with friends today?
4. There are many festivals in Vietnam **and** many of them are held in the spring.
5. Did you stay at home last night **or** did you go out with your friends?
6. I broke my glasses yesterday, **so** I didn’t see things clearly.
7. My brother doesn’t socialize much, **but** he has very few friends.
8. A new camera is all I want now, **but** I don’t have enough money.
9. Mary looks small and thin, **yet** she shows great strength.
10. I have many things to do tonight, **so** I reject my friend’s invitation to her party.
11. My computer is brand new, **but** I encounter some problems when I use it.
12. This is a complex problem, **so** we need to work together to find the solution.
13. Peter doesn’t feel well today, **so** he is absent from school.
14. They thought they won the match, **but** it turned out that they were losers.
15. My siblings and I don’t share many similarities, **but** we are in harmony with each other.

Feel free to ask if you need further clarification!