Let's analyze the stress patterns of the words in each set:

### Set 1:
1. **Ancient**: Stress on the first syllable: **AN**-cient
2. **Basic**: Stress on the first syllable: **BA**-sic
3. **Observe**: Stress on the second syllable: ob-**SERVE**
4. **Structure**: Stress on the first syllable: **STRUC**-ture

In this set, **Observe** (C) has a different stress pattern from the others. The other words are stressed on the first syllable.

### Set 2:
1. **Continue**: Stress on the second syllable: con-**TIN**-ue
2. **Recognise**: Stress on the second syllable: rec-**OG**-nise
3. **Concentrate**: Stress on the first syllable: **CON**-cen-trate
4. **Occupy**: Stress on the second syllable: oc-**CU**-py

In this set, **Concentrate** (C) has a different stress pattern from the others. The other words are stressed on the second syllable.

### Summary
- For the first set, the word with a different stress pattern is **C. Observe**.
- For the second set, the word with a different stress pattern is **C. Concentrate**.