def pick_rarifaction_level(id_, lookups):
    """Determine which lookup has the appropriate key

    id_ is a barcode, e.g., '000001000'
    lookups is a list of tuples, e.g., [('10k',{'000001000':'000001000.123'})]

    The order of the lookups matters. The first lookup found with the key will
    be returned.

    None is returned if the key is not found
    """
    for name, lookup in lookups:
        if id_ in lookup:
            return name
    return None