他向导师郑重起誓，一定会完成那项未竟的研究。
He made a solemn vow to his mentor that he would complete the unfinished research.
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解释
形容承诺或誓言严肃、真诚、不可违背。
He made a solemn vow to his mentor that he would complete the unfinished research.
形容承诺或誓言严肃、真诚、不可违背。