皮肤是保护我们身体的第一道防线，在皮肤的结构及附属物中，与皮肤保护功能无关的是（　　）

下列各句中，语言得体的一句是  (　　)

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    Is there link between humans and climate change or not? This question was first studied in the early 1900s. Since then, many scientists have thought that our actions do make a difference. In 1997, the Kyoto Protocol explained our role in the Earth's changing atmosphere and set international limits for gas emissions(排放) from 2008 to 2012. Some countries have decided to continue these reductions until 2020. More recently, the Paris Agreement, stuck by nearly 200 countries, also aims to limit global warming. But just now how much warmer it will get depends on how deeply countries cut carbon emissions.

下列命题中：
①$\overrightarrow{a}$∥$\overrightarrow{b}$$\iff$存在唯一的实数$\lambda \in R$，使得$\overrightarrow{b}=\lambda \overrightarrow{a}$
②$\overrightarrow{e}$为单位向量，且$\overrightarrow{a}$∥$\overrightarrow{e}$，则$\overrightarrow{a}$=±|$\overrightarrow{a}$|·$\overrightarrow{e}$；③$\left|\overrightarrow{a}·\overrightarrow{a}·\overrightarrow{a}\right|={\left|\overrightarrow{a}\right|}^3$；
④$\overrightarrow{a}$与$\overrightarrow{b}$共线，$\overrightarrow{b}$与$\overrightarrow{c}$共线，则$\overrightarrow{a}$与$\overrightarrow{c}$共线；⑤若$\overrightarrow{a}·\overrightarrow{b}=\overrightarrow{b}·\overrightarrow{c}$且$\overrightarrow{b}\ne \overrightarrow{0}$，则$\overrightarrow{a}=\overrightarrow{c}$
其中正确命题的序号是                 (     )