沙漠里的绿洲，水从哪来？

Deserts look dry and empty. 沙漠看上去又干又空。 But under the sand, water hides. 可沙子底下藏着水。 Sometimes the water pushes up to the surface. 有时候，地下水会涌出地面。 Then grass and trees start to grow. 于是草和树就长了出来。 This green spot is called an oasis. 这块绿色的地方叫绿洲。 Travelers can rest and drink there. 赶路的人可以在这儿歇脚喝水。