Sure, let's analyze each set of words to determine which one doesn't belong:

1. **A. crowded**               **B. quiet**                      **C. busy**                    **D. city**

- **A, B, and C** are adjectives describing the state or condition of a place.
- **D** is a noun referring to a type of place.
- **Choose out:** **D. city**

2. **A. town**                     **B. village**                        **C. modern**                        **D. country**

- **A, B, and D** are nouns referring to types of places.
- **C** is an adjective describing a characteristic.
- **Choose out:** **C. modern**

3. **A. live**                       **B. street**                        **C. lane**                        **D. district**

- **B, C, and D** are nouns referring to types of places or areas.
- **A** is a verb.
- **Choose out:** **A. live**

4. **A. mountain**                      **B. pretty**                        **C. island**                        **D. town**

- **A, C, and D** are nouns referring to types of places or geographical features.
- **B** is an adjective.
- **Choose out:** **B. pretty**

So, the words that don't belong in each set are:
1. **D. city**
2. **C. modern**
3. **A. live**
4. **B. pretty**