What are the two sub-types of a polar climate?

There are two types of polar climate: ET, or tundra climate; and EF, or ice cap climate. A tundra climate is characterized by having at least one month whose average temperature is above 32 °F, while an ice cap climate has no months above 32 °F.[2][clarification needed] In a tundra climate, trees cannot grow, but other specialized plants can grow. In an ice cap climate, no plants can grow, and ice gradually accumulates until it flows elsewhere. Many high altitude locations on Earth have a climate where no month has an average temperature of  50 °F or higher, but as this is due to elevation, this climate is referred to as Alpine climate. Alpine climate can mimic either tundra or ice cap climate.

the correct answer is - d. china has a large and growing population.

the fact that china has a large (the biggest) population, and it is still growing, doesn't hinder the agriculture production in the country. in fact, it can for increased production in the agriculture, since there's more labor force, as well the sheer mass of people produces lots of scientists that come up with new inventions as to how to improve this sector. nice example is the inner mongolia region in china, in general dominated by the gobi desert, but few scientist came up with a nice idea as to how to make the region productive by using plants that are very resistant to droughts, so lots of people have been employed, and the region is becoming greener and greener each year, and the production of food in this region is also increasing.