问题
单项选择题
If x, y, and w are nonzero numbers and x-y=w, which of the following is equal to 1 ？（）
A.A
B.B
C.C
D.D
E.E
答案
参考答案：A
解析：
Add y to and subtract w from both sides of the equation x-y=w and you get x-w=y, so 
.