题干

玉米是一年生雌雄同株异花授粉植物,其籽粒的颜色受两对等位基因A,a和B,b控制.A基因存在时,能合成酶Ⅰ;B基因存在时,酶Ⅱ的合成受到抑制.籽粒颜色的转化关系为:白色 黄色 紫色.

研究发现纯合紫粒玉米的花粉完全败育,不具备受精能力,其它类型玉米的花粉正常.将杂合白粒玉米和纯合紫粒玉米进行间行种植,F1中收获得到的玉米共有三种类型:白粒、黄粒和紫粒.回答下列问题:

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阅读下面短文,从A、B、C、D四个选项中选出最佳选项。

    The government in China ended his one-child policy and let families have two children instead in 2015.

    A Chinese Communist Party statement gave a number of reasons for the change in policy. The statement said the change is meant to balance population development, stop a falling birth rate(出生率)and strengthen the country's labor force(劳动力). China, with the largest population in the world, started the one-child policy in 1980. 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 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 teacher and population expert, explained how Chinese families react(反应) to the newest policy. "Too many young people in the cities are no longer interested in having a second child," he said. "People in the countryside are more interested. But some of them are already allowed to have two children." At the end of 2014, China had a population of 1.37 billion people. A total of 800 million of them have jobs. But the labor market need of labor by the year 2050. With the two-child policy, an increase in births can solve this problem.

    Boys and girls, what do you think of the two-child policy? Do you want to have a new-born brother or sister?