①若 $\overrightarrow{a}$ =2 $\overrightarrow{b}$ ，则 $\overrightarrow{a}$ 、 $\overrightarrow{b}$ 线性相关；

②若 $\overrightarrow{a}$ 、 $\overrightarrow{b}$ 为非零向量，且 $\overrightarrow{a}$ ⊥ $\overrightarrow{b}$ ，则 $\overrightarrow{a}$ 、 $\overrightarrow{b}$ 线性相关；

③若 $\overrightarrow{a}$ 、 $\overrightarrow{b}$ 线性相关， $\overrightarrow{b}$ 、 $\overrightarrow{c}$ 线性相关，则 $\overrightarrow{a}$ 、 $\overrightarrow{c}$ 线性相关；

④向量 $\overrightarrow{a}$ 、 $\overrightarrow{b}$ 线性相关的充要条件是 $\overrightarrow{a}$ 、 $\overrightarrow{b}$ 共线．

上述命题中正确的是____（写出所有正确命题的编号）

人类起源于（   ）

阅读下列短文，从下面每小题的A、B、C、D四个选项中选出最佳选项。

    A group of eight students from Shenzhen Middle School won the gold medal at the 2017 United States International Youth Physics Competition on January 31. It was the second time for the school to win the prize after its first championship in 2013.

    All of the open-ended projects studied at the competition are beyond the normal standard at high schools. Shenzhen Middle School is the only high school in China that has won the gold medal.

    The competition this year attracted 11 top high schools in the United States and China, including Harker School and Philips Exeter University in the United States as well as the Middle School Affiliated with Renmin University of China（人大附中）and Nanjing Foreign Languages School in China.

    The Shenzhen Middle School team went through a two-day debate with the other teams in English about four physics projects that they had studied for a whole year.

The school said that the team prepared for a whole year, from raising theoretical（理论） models to designing experiments, which greatly developed the students' abilities to work and think like real scientists.

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