Sure, let's analyze the pronunciation and stress patterns for each set of words:

1. **A. back**       B. taxi        C. last      D. parents
- A. back /bæk/ - short "a" sound
- B. taxi /ˈtæksi/ - short "a" sound
- C. last /læst/ - short "a" sound
- D. parents /ˈpeərənts/ - the "a" here is pronounced as /eə/

The word with a different pronunciation is **D. parents**.

2. **A. Coach**    B. Ancient     C. Come      D. Country
- A. coach /koʊtʃ/ - "c" pronounced as /k/
- B. ancient /ˈeɪnʃənt/ - "c" pronounced as /ʃ/
- C. come /kʌm/ - "c" pronounced as /k/
- D. country /ˈkʌntri/ - "c" pronounced as /k/

The word with a different pronunciation is **B. ancient**.

3. **A. Motorbike**   B. Countryside   C. Underground  D. Information
- A. motorbike /ˈmoʊtərˌbaɪk/ - primary stress on the first syllable
- B. countryside /ˈkʌntriˌsaɪd/ - primary stress on the first syllable
- C. underground /ˈʌndərˌɡraʊnd/ - primary stress on the first syllable
- D. information /ˌɪnfərˈmeɪʃən/ - primary stress on the third syllable

The word with a different stress pattern is **D. information**.

I hope this helps! Let me know if you need further assistance.