题目解析:
A选项用rainfall,B选项用melting snow定位到:
Rainfall was limited, and what water there was rushed across the plain in the annual flood of melted snow.
AB选项和原文呼应,所以不选。
C选项用silt定位到:
Once this was done and the silt carried down by the rivers was planted, the rewards were rich: four to five times what rain-fed earth would produce.
这里说了带来的回报是丰厚的。所以C选项的damaged crops很原文说反,选C。
D选项的stone, metal对应到:
There were few natural resources, no timber, stone, or metals.
D正确,不选。