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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:

def _get_repo_options_env(env):
    '''
    Get repo environment overrides dictionary to use in repo options process

    env
        A dictionary of variables to define the repository options
        Example:

        .. code-block:: yaml

            - env:
                - OPTIONS : 'ask-passphrase'

        .. warning::

            The above illustrates a common PyYAML pitfall, that **yes**,
            **no**, **on**, **off**, **true**, and **false** are all loaded as
            boolean ``True`` and ``False`` values, and must be enclosed in
            quotes to be used as strings. More info on this (and other) PyYAML
            idiosyncrasies can be found :ref:`here <yaml-idiosyncrasies>`.

    '''
    env_options = ''
    if env is None:
        return env_options
    if not isinstance(env, dict):
        raise SaltInvocationError(
            '\'env\' must be a Python dictionary'
        )
    for key, value in env.items():
        if key == 'OPTIONS':
            env_options += '{0}\n'.format(value)
    return env_options