The correct answer is - c. an aging population that the government must support.
China has been trying to discourage the population growth in the country for around half a century now, and while it may be good for lots of reasons considering the size of the country's population, it might affect the economy in the future in a pretty bad way. If this trend continues, it means that relatively soon, China's age demographic picture will change drastically, where the percentage of the old population will constantly grow, thus having an aging population. This population will be taking pensions, and those money go through the government, which means the country will have to provide enormous amount of money each year, and as the time passes, more and more as well, in order to support them. Considering the sheer size of the population of the country, pretty soon we can be talking about a number of 150-200 million people that will be living on state money.