If there were no family planning, China, a country of the largest population, would have its population tens of millions greater.
=Without the family planning
policy / If it were not for the family planning policy, China, a country with the largest population, would have had.这句是和现在情况相反的吧？用would加动词原形
计划生育是过去实施的，和过去相反？？？从现实来看 计划生育政策实施多年 属于过去发生的动作 应该是对过去的虚拟

现在政策不是放宽了么与过去事实相反\x09had + 过去分词？