河西走廊地区的灌溉水源主要指：（  ）

根据句意及汉语提示，填入适当单词完成下列句子。 
（1）There are many trees and ____(灌木从)in the garden.
（2）There are some ____ (抢劫者)in the building.
（3）People have different ____(能力).
（4）It's ____  (必要的)to give them clean water if you want them to be healthy.
（5）How ____ (可怕的) the traffic was!

若$x=2+\sqrt{3}$， $y=\frac{1}{2-\sqrt{3}}$则x与y关系是（      ）