请教一道数学题

The annual rent collected by a corporation from a certain building was x percent more in 1998 than in 1997 and y percent less in 1999 than in 1998.  Was the annual rent collected by the corporation from the building more in 1999 than in 1997?

(1)     x > y     

(2)     xy/100 < x – y

A. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.

B. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.

C. BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.

D. EACH statement ALONE is sufficient.

E. Statements (1) and (2) TOGETHER are NOT sufficient.

Key是 B

请问为什么? 谢谢!!!!!!

1998 －1997 ＝X% 1997

1999－1998＝－Y%1998=-y%(1+x%)1997

=-1997(y%+x%y%)

1999-1997 =(1999-1998)+(1998-1997)=1997(x%-y%-x%y%)

x/100-y/100-  xy /10000 = 1/100(x-y- xy/100)

1/100 >0  soif x-y >xy/100   1999-1997 >0

if x-y......<           <0