The north china plain was built up of soil and deposits.

It is true that the North China Plain was built up of soil and deposits. This soil and deposit come from the river Huang He, or the Yellow River in English, located in China, flowing through its 9 provinces before emptying into the Bohai Sea. The North China Plain is the largest alluvial plain in China. 

Ithink the answer is b. shakeri hope im not wrong : )