C

    The government in China plans to end its one-child policy (政策) and let families have two children instead. The plan was meant to balance (平衡) population development and stop a falling birth rate (出生率).

    China started the one-child policy in the 1980s. But the government allowed only a small number of couples to have two children. For example, some families in the countryside could have two children, if the first-born child is a girl. In 2013, the Chinese government gave other couples a chance to have two children if one of them was an only child.

    Jiang Quanbao, a population expert, explained how Chinese families react to the newest policy. "Lots of young people in the cities are no longer interested in having a second child," he said.

    At the end of 2014, China had a population of 1.37 billion people. But the labor market population will drop in 35 years. That is to say, the country will be in great need of labor by the year 2050. With the "two children" policy, an increase in births can solve this problem.

①﹣3是函数y=f（x）的极值点；

②﹣1是函数y=f（x）的最小值点；

③y=f（x）在x=0处切线的斜率小于零；

④y=f（x）在区间（﹣3，1）上单调递增．

则正确命题的序号是____．

①人 ②阳光 ③蚜虫 ④空气 ⑤田鼠 ⑥水 ⑦蚯蚓 ⑧土壤．