计划生育 family planning
基本国策 a basic national/state policy
制定政策 to make a policy
（政策）生效，开始实施 to come into force/effect
晚婚晚育 late marriage and late childbirth
居住证 residence permit
少数民族 ethnic minority
过快增长 excessive growth
出生率 birth rate
人口素质 quality of the population
人口老龄化 aging of the population
老龄化社会 aging society
小康社会 well-off society
推行可持续发展战略 to pursue the strategy of sustainable development
1.A number of factors are accountable for this situation.
A number of factors might contribute to (lead to )(account for ) the phenomenon(problem).
2. The answer to this problem involves many factors.
3. The phenomenon mainly stems from the fact that...
4. The factors that contribute to this situation include...
5. The change in ...largely results from the fact that...
6. We may blame ...,but the real causes are...
7. Part of the explanations for it is that ...
One of the most common factors (causes ) is that ...
Another contributing factor (cause ) is ...
Perhaps the primary factor is that …
But the fundamental cause is that