------
## 最终结论
```python
def sort_third(l: list):
    sortable_elements = [l[i] for i in range(len(l)) if i % 3 == 0]
    sortable_elements.sort()
    
    result = l[:]
    for index, value in enumerate(sortable_elements):
        result[index * 3] = value
        
    return result
```