------
## 最终结论
```python
def Extract(lst):
    return [sublist[0] for sublist in lst]

# Test cases
assert Extract([[1, 2], [3, 4, 5], [6, 7, 8, 9]]) == [1, 3, 6]
assert Extract([[1,2,3],[4, 5]]) == [1,4]
assert Extract([[9,8,1],[1,2]]) == [9,1]
```