The dividing line between the north and the south of China is the Qinling Mountains and the Huaihe River. The main sugar crop in the Northeast Plain is sugar beet, which is located in the northern part of China. The natural environment in Qinghai-Tibet region is extremely cold.

So the answer is:

(1) Qinling-Huaihe River;

(2) sugar beet; North;

(3)

(4) cold.