Extensions are not a required feature of the grammar and, thus, their syntax is not as well defined as the other constructs of the language.

扩展并不是文法必需的特性，因此它们的语法不象该语言的其它构造那样得到良好定义。

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Honeycombing is usually subpleural and is characterized by well-defined walls. It is a ct feature of established pulmonary fibrosis.

蜂窝常位于胸膜下，有清楚的壁为其特征，它是一种可确定为肺纤维化的CT征象。

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