Linguists call a single unit of meaning, whether "tree" or "UN -", a morpheme, and some languages bind them together obligatorily.

语言学家把一个语义单位称作一个词素，如“tree(树)”，或“un -(前缀“否”)”。一些语言将词素结合在一起。

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Human Demodex is a permanent parasitic mite that is obligatorily harbors in hair follicles and in pilosebaceous glands of human skin, especially human facial skin.

人体蠕形螨是专性寄生在人体毛囊和皮脂腺的一种永久性寄生螨，以面部为主。

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Due to limitation of pages, the "obligatorily read" content of the local newspapers is reduced and a few newspapers have to add pages, but the proportion of news is decreasing.

地方报纸由于版面所限，“必读性”内容减少，少数报纸不断扩版但新闻比重不断降低。

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