Here are the words that differ from the others in terms of the position of primary stress:

1. **C. Unusual** - The stress is on the second syllable (un-**U**-sual) while the others have stress on the second syllable.

2. **A. Comer** - The stress is on the first syllable (**COM**-er), while the others have stress on the second syllable.

3. **C. Karate** - The stress is on the second syllable (ka-**RA**-te), while the others are on the second or have a primary stress pattern that differs slightly.

4. **C. Tomorrow** - The stress is on the second syllable (to-**MOR**-row), while the others have stress on the first syllable.

5. **B. Writer** - The stress is on the first syllable (**WRIT**-er), while the others have stress on the second syllable.

So the circled answers would be:

1. C
2. A
3. C
4. C
5. B