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。