Here are the answers to both sections of the questions you've provided:

### I. Choose the best option for pronunciation:
1. **C. competition**
2. **C. character**
3. **C. close**
4. **C. carbon**
5. **D. thunder**

### II. Mark the letter A, B, C, or D to indicate the word that differs from the other three in the position of primary stress:
1. **A. machine** (the stress is on the second syllable, while others are on the first)
2. **C. information** (the stress is on the third syllable, while others are on different syllables)
3. **C. encourage** (the stress is on the second syllable, while others are on the first)
4. **C. electronic** (the stress is on the second syllable, while others are on the first)

Feel free to ask if you have more questions!