已知向量$\overrightarrow{a}=\left(-1,x,3\right)$，$\overrightarrow{b}=\left(2,-4,y\right)$，且$\overrightarrow{a}//\overrightarrow{b}$，那么$x+y$等于（    ）

Thousands of years ago，human(人类)didn’t live in towns．Sometimes they would live in caves(洞穴)or build camps in the forest．
Only about thirty people1 in each camp．The men would go hunting while the woman and children2food from trees around the camp．All the food was 3 among people in the group．Every few weeks they moved to another place to find more food．It was a simple life，but people had to be 4 .They had to make everything that they needed，and they had to know a lot about plants and animals．
Nowadays most people live in towns and cities，and they work in offices and factories．Life is 5than in the old days．There are fewer 6，but there is less excitement．Some people go7  excitement  sailing round the world．climbing mountains，or exploring(探测)caves．
Most people look forward to the8,a time when they can enjoy a change from the normal life．For some this means going camping．But camping today is 9 from camping in the past．Gas cookers，ready-made food and air-beds mean people can camp much more10 than they did in the old times．

综合性学习。

      中华文化源远流长，传统美德薪火相传。学校准备开展一次以“倡导社会主义核心价值观，争做美德少年”为主题的综合实践活动，请你参与，按要求完成任务。

“人心齐，泰山移。”社会生活中，谁都不可能脱离群体而单独存在，因为个人的力量毕竟是有限的，个人或群体之间为达到共同的目的需要彼此合作。下列关于合作说法正确的是（　　）
①合作是共享的基础，共享是合作的必然结果       ②合作的目的在于超越对方，打败竞争对手
③我们合作的核心是发扬集体主义精神                ④合作虽然需要，但势必会削弱竞争，阻碍更快地进步