China had a larger population than any other country in the world转换成其他两句一样的

China had a larger population than any other country in the world
转换成其他两句一样如下:
China's population is larger than any other country in the world.
No country in the world has a population larger than China.
larger 是比较级 largest 是最高级.提问说要比较级,所以句子只能用 larger,是吗?
若你要用largest 同义的第二句:
那麼,The country with the largest population of the world is China.可以吗?能说一说population前为什么加A么言是文法上要求的介词。