Sure, let's analyze the pronunciation of the underlined parts in each set of words:

1. **A. distr**i**bute**     B. tr**i**be         C. tr**i**angle     D. tr**i**al
- A. distribute: /dɪˈstrɪb.juːt/
- B. tribe: /traɪb/
- C. triangle: /ˈtraɪ.æŋ.ɡəl/
- D. trial: /ˈtraɪ.əl/
- The underlined part in "distribute" is pronounced /ɪ/, while in the other words it is pronounced /aɪ/. So, the answer is **A. distribute**.

2. **A. pr**o**fit**         B. pr**o**fession   C. pr**o**mise    D. p**o**verty
- A. profit: /ˈprɒf.ɪt/
- B. profession: /prəˈfeʃ.ən/
- C. promise: /ˈprɒm.ɪs/
- D. poverty: /ˈpɒv.ə.ti/
- The underlined part in "profession" is pronounced /ə/, while in the other words it is pronounced /ɒ/. So, the answer is **B. profession**.

3. **A. plough**ed**     B. laugh**ed**      C. cough**ed**   D. lock**ed**
- A. ploughed: /plaʊd/
- B. laughed: /læft/
- C. coughed: /kɒft/
- D. locked: /lɒkt/
- The underlined part in "ploughed" is pronounced /d/, while in the other words it is pronounced /t/. So, the answer is **A. ploughed**.

4. **A. st**ea**dy**         B. r**ea**dy         C. br**ea**kfast   D. st**ea**k
- A. steady: /ˈstɛd.i/
- B. ready: /ˈrɛd.i/
- C. breakfast: /ˈbrɛk.fəst/
- D. steak: /steɪk/
- The underlined part in "steak" is pronounced /eɪ/, while in the other words it is pronounced /ɛ/. So, the answer is **D. steak**.

5. **A. descri**b**e**     B. cele**b**rate   C. plum**b**er     D. a**b**rupt
- A. describe: /dɪˈskraɪb/
- B. celebrate: /ˈsɛl.ɪ.breɪt/
- C. plumber: /ˈplʌm.ər/
- D. abrupt: /əˈbrʌpt/
- The underlined part in "plumber" is silent, while in the other words it is pronounced /b/. So, the answer is **C. plumber**.

So the answers are:
1. A. distribute
2. B. profession
3. A. ploughed
4. D. steak
5. C. plumber