To find the word which has a different sound in the underlined part, let's analyze each set of words:

1. A. prefer
B. better
C. teacher
D. worker

The underlined part is "er":
- prefer: /pɹɪˈfɜːr/
- better: /ˈbɛtər/
- teacher: /ˈtiːtʃər/
- worker: /ˈwɜːrkər/

The different sound is in "prefer" (A).

2. A. bear
B. hear
C. dear
D. near

The underlined part is "ear":
- bear: /bɛər/
- hear: /hɪər/
- dear: /dɪər/
- near: /nɪər/

The different sound is in "bear" (A).

3. A. collect
B. concern
C. concert
D. combine

The underlined part is "co":
- collect: /kəˈlɛkt/
- concern: /kənˈsɜːrn/
- concert: /ˈkɒnsərt/
- combine: /kəmˈbaɪn/

The different sound is in "concert" (C).

4. A. absent
B. government
C. dependent
D. enjoy

The underlined part is "en":
- absent: /ˈæbsənt/
- government: /ˈɡʌvərnmənt/
- dependent: /dɪˈpɛndənt/
- enjoy: /ɪnˈdʒɔɪ/

The different sound is in "enjoy" (D).

5. A. future
B. return
C. picture
D. culture

The underlined part is "ure":
- future: /ˈfjuːtʃər/
- return: /rɪˈtɜːrn/
- picture: /ˈpɪktʃər/
- culture: /ˈkʌltʃər/

The different sound is in "return" (B).

So, the words with different sounds in the underlined parts are:
1. A. prefer
2. A. bear
3. C. concert
4. D. enjoy
5. B. return