------
## 最终结论
```python
def extract_string(string_list, size):
    return [s for s in string_list if len(s) == size]

# Test cases
assert extract_string(['Python', 'list', 'exercises', 'practice', 'solution'], 8) == ['practice', 'solution']
assert extract_string(['Python', 'list', 'exercises', 'practice', 'solution'], 6) == ['Python']
assert extract_string(['Python', 'list', 'exercises', 'practice', 'solution'], 9) == ['exercises']
```