∵$$\left\textbar{} a \right\textbar=-a$$，∴$$a\leqslant 0$$．  $$\left\textbar{} a-1 \right\textbar-\left\textbar{} a-2 \right\textbar=-\left( a-1 \right)+\left( a-2 \right)=-1$$，选$$\text{A}$$． 
已知$$\left\textbar{} a \right\textbar=-a$$，则化简$$\left\textbar{} a-1 \right\textbar-\left\textbar{} a-2 \right\textbar$$所得的结果是（~ ）．

A) $$-1$$ 
B) $$1$$ 
C) $$2a-3$$ 
D) $$3-2a$$ 