Sure! Here are the best answers for the sentences based on the provided options:

1. **You should __________ information about a custom or tradition.**
**Answer:** **C. finding**

2. **A custom is something that has become an __________ way of doing things.**
**Answer:** **D. accepted**

3. **In the UK, there are lots of customs for table manners. For example, we __________ a knife and fork at dinner.**
**Answer:** **A. have to**

4. **In Vietnam, you __________ use only the first name to address people older than you.**
**Answer:** **C. shouldn’t**

So the complete answers look like this:
1. C
2. D
3. A
4. C