一道gmat逻辑题,看着答案想不通啊.求教啊.

一道gmat逻辑题,看着答案想不通啊.求教啊.
A ten-year comparison between the United States and the Soviet Union in terms of crop yields per acre revealed that when only planted acreage is compared,Soviet yields are equal to 68 percent of United States yields.When total agricultural acreage(planted acreage plus fallow acreage)is compared,however,Soviet yield is 114 percent of United States yields.
From the information above,which of the following can be most reliably inferred about United States and Soviet agriculture during the ten-year period?
(A)A higher percentage of total agriculture acreage was fallow in the United States than in the Soviet Union.
(B)The United States had more fallow acreage than planted acreage.
(C)Fewer total acres of available agricultural land was fallow in the Soviet Union than in the United States.
(D)The Soviet Union had more planted acreage than fallow acreage.
(E)The Soviet Union produced a greter volume of crops than the United States produced.
正确答案是A
X表示苏联粮食总产量 A表示苏联计划种植面积 A'表示FALLOW ACREAGE,Y B B'表示美国的对应数据,X/A=0.68Y/B,X/(A+A')=1.14Y/(B+B')
因为X/(A+A')＞Y/(B+B'),所以A'在A+A'中占的比例就比B'在B+B'中的比例要小,所以A正确
我的问题是为什么 “因为X/(A+A')＞Y/(B+B'),所以A'在A+A'中占的比例就比B'在B+B'中的比例要小” 这个怎么推出来的?我怎么想都想不通啊.