from typing import List


def get_header_col(board: List[List[str]]) -> List[str]:
    """
        Get the column header.
        (Note: this list should only contain alphabet.)

        Parameters
        ----------
        board: List[List[str]]
            2D array containing all the game detail, including column header, row header and placed buildings.

        Returns
        -------
        col_header_list: List[str]
            A list containing all the column header.
    """

    return board[0]