def remove_variables(data, exclude_variables=None):
    """    
    Removes variables from the data set.

    If passed a list of variable names to exclude, remove_variables
    will drop those variables from the dataset.

    :param data: A pandas.DataFrame.
    :param exclude_variables: A list of strings.
    :return: A pandas.DataFrame.
    """
    if exclude_variables is not None:
        data = data.drop(exclude_variables, axis=1)
    return data