选择合适的标点符号可以让段落层次更加清晰

根据句子之间的相互关系选择合适的标点符号可以让段落层次更加清晰，使读者更加容易把握文章所要表达的意思。

比如要用英文表达以下内容：

收集2012年2月至2014年4月期间就诊的260例肺炎患儿入院24 h内的NPA及BALF，荧光定量PCR法检测NPA和BALF中的MP-DNA，在入院24 h内及治疗8~12 d时采集所有患儿静脉血，ELISA法检测血清MP-IgM。

第一个版本如下。这个版本基本上是按照中文意思翻译成了4句话，层次不是太清晰。

The Nasopharyngeal aspirates (NPA) and bronchoalveolar lavage fluid (BALF) of 260 children with pneumonia admitted to our hospital from February 2012 to April 2014 were collected within 24 hours of admission. Mycoplasma pneumoniae (MP) DNA in NPA and BALF was measured by quantitative real-time PCR. Venous blood of these children was also collected within 24 hours of admission and on days 8-12 of treatment. Serum MP-IgM was measured using ELISA.

第二个版本如下。这个版本把中文里的第一句话拆分成了两句话，即专门用一句话介绍了研究对象，然后才是研究方法的介绍。但是研究方法部分的结构不是太清晰。

A total of 260 children with pneumonia admitted to our hospital from February 2012 to April 2014 were enrolled. Nasopharyngeal aspirates (NPA) and bronchoalveolar lavage fluid (BALF) of these children were collected within 24 hours of admission. Mycoplasma pneumoniae (MP) DNA in NPA and BALF was measured by quantitative real-time PCR. Venous blood of these children was also collected within 24 hours of admission and on days 8-12 of treatment. Serum MP-IgM was measured using ELISA.

第三个版本如下。方法部分由两个小部分组成，收集NPA及BALF与检测MP-DNA是第一个小部分，所以之前的两个句子变成两个分句，中间用“逗号+and”连接；采集静脉血和检测MP-IgM是第二个小部分，之前的两个句子变成两个分句，中间也用“逗号+and”连接。

A total of 260 children with pneumonia admitted to our hospital from February 2012 to April 2014 were enrolled. Nasopharyngeal aspirates (NPA) and bronchoalveolar lavage fluid (BALF) of these children were collected within 24 hours of admission, and Mycoplasma pneumoniae (MP) DNA in NPA and BALF was measured by quantitative real-time PCR. Venous blood of these children was also collected within 24 hours of admission and on days 8-12 of treatment, and serum MP-IgM was measured using ELISA.

此外，还可以使用分号代替逗号“+and”。

A total of 260 children with pneumonia admitted to our hospital from February 2012 to April 2014 were enrolled. Nasopharyngeal aspirates (NPA) and bronchoalveolar lavage fluid (BALF) of these children were collected within 24 hours of admission; Mycoplasma pneumoniae (MP) DNA in NPA and BALF was measured by quantitative real-time PCR. Venous blood of these children was also collected within 24 hours of admission and on days 8-12 of treatment; serum MP-IgM was measured using ELISA.

也可以考虑使用不定式。

A total of 260 children with pneumonia admitted to our hospital from February 2012 to April 2014 were enrolled. Nasopharyngeal aspirates (NPA) and bronchoalveolar lavage fluid (BALF) of these children were collected within 24 hours of admission to measure Mycoplasma pneumoniae (MP) DNA in NPA and BALF by quantitative real-time PCR. Venous blood of these children was also collected within 24 hours of admission and on days 8-12 of treatment to measure serum MP-IgM using ELISA.

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