黃金閱讀 Desert Formation - 英檢

The final major human cause of desertification is soil salinization
resulting from overirrigation. Excess water from irrigation sinks down
into the water table. If no drainage system exists, the water table
rises, bringing dissolved salts to the surface. The water evaporates and
the salts are left behind, creating a white crustal layer that prevents air
and water from reaching the underlying soil.

9. All of the following are mentioned in the passage as contributing
to desertification EXCEPT
(1)Soil erosion
(2)Global warming
(3)Insufficient irrigation
(4)The rising of livestock

這題答案是(2)

我一看到有跟overirrigation相反的答案就選了，原文中說desertification
一個重要原因是overirrigation，後來看一下原文其他部分的確沒有提到
Global warming，但不知道為何Insufficient irrigation錯?

謝謝大家!

--