这对在外工作，而必须找到一位保姆或其它儿童护理提供者的父母尤其困难，因为后者会坚持他们认为最为重要的一些礼节。
This poses a particular challenge for parents who work outside the home and must find a sitter, nanny or other child-care provider who will insist on the manners they consider most important.
耐药性是为了实现使用化学疗法成功治疗人类肿瘤而必须克服的最困难的问题之一。
Drug resistance is one of the most difficult problems that must be overcome in order to achieve successful treatment of human tumors with chemotherapy.
耐药性是为了实现使用化学疗法成功治疗人类肿瘤而必须克服的最困难的问题之一。
Drug resistance is one of the most difficult problems that must be overcome in order to achieve successful treatment of human tumors with chemotherapy.
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