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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 summarize( text: str, n: int, engine: str = "frequency", tokenizer: str = "newmm" ) -> List[str]: """ Thai text summarization :param str text: text to be summarized :param int n: number of sentences to be included in the summary :param str engine: text summarization engine :param str tokenizer: word tokenizer :return List[str] summary: list of selected sentences """

    sents = []

    if engine == "frequency":
        sents = FrequencySummarizer().summarize(text, n, tokenizer)
    else:  # if engine not found, return first n sentences
        sents = sent_tokenize(text)[:n]

    return sents