def METHOD_NAME(tb: Table) -> Table:
    """Add annual change variables to combined BP & Shift dataset.
    Parameters
    ----------
    tb : Table
        Combined BP & Shift dataset.
    Returns
    -------
    combined : Table
        Combined BP & Shift dataset after adding annual change variables.
    """
    combined = tb.copy()
    # Calculate annual change.
    combined = combined.sort_values(["country", "year"]).reset_index(drop=True)
    for cat in ("Coal", "Oil", "Gas"):
        combined[f"Annual change in {cat.lower()} production (%)"] = (
            combined.groupby("country")[f"{cat} production (TWh)"].pct_change() * 100
        )
        combined[f"Annual change in {cat.lower()} production (TWh)"] = combined.groupby("country")[
            f"{cat} production (TWh)"
        ].diff()
    return combined