因为$$a\textless{}0$$，所以$$\left\textbar{} a \right\textbar=-a$$．  因为$$b\textgreater0$$，所以$$\left\textbar{} b \right\textbar=b$$．  所以$$a+b=-\left\textbar{} a \right\textbar+\left\textbar{} b \right\textbar$$．选$$\text{A}$$． 
若$$a\textless{}0$$，$$b\textgreater0$$，且$$\left\textbar{} a \right\textbar\textless{}\left\textbar{} b \right\textbar$$，则$$a+b=$$（~ ）．

a) $$\left\textbar{} b \right\textbar-\left\textbar{} a \right\textbar$$ 
b) $$-\left\textbar{} a \right\textbar-\left\textbar{} b \right\textbar$$ 
c) $$\left\textbar{} a \right\textbar-\left\textbar{} b \right\textbar$$ 
d) $$\left\textbar{} a \right\textbar+\left\textbar{} b \right\textbar$$ 