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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 _add_reference(reference, statement):
    '''
    Adds a reference to statement.
    '''
    type_, value = _expand_one_key_dictionary(reference)
    opt = Option(type_)
    param = SimpleParameter(value)
    opt.add_parameter(param)
    statement.add_child(opt)