题目：下列计算正确的是 ( )
选项：
bullet: A
text: 1+\frac{1}{a}=\frac{2}{a}
bullet: B
text: \frac{-a-b}{a+b}=-1
bullet: C
text: (1- \frac{1}{a+1})(a+1)= \frac{1}{a}
bullet: D
text: \frac{1}{a-b}-\frac{1}{b-a}=0
答案：B
解析：解:A:因为1+ \frac{1}{a}= \frac{a}{a}+\frac{1}{a}= \frac{a+1}{a}，所以A选项错误; B:因为 \frac{-a-b}{a+b}= \frac{-(a+b)}{a+b}=-1，所以B选项正确; C:因为(1- \frac{1}{a+1})(a+1)=( \frac{a+1}{a+1}-\frac{1}{a+1})(a+1)= \frac{a}{a+1}(a+1)=a，所以C选项错误; D因为 \frac{1}{a-b}-\frac{1}{b-a}=\frac{1}{a-b}+\frac{1}{a-b}=\frac{2}{a-b}，所以D选项错误. 故选:B.