设变量 $x,y$满足 $\{\begin{array}{c}x+y\le 1\\ x-y\le 1\\ x\ge 0\end{array}$，则 $x+2y$的最大值和最小值分别为(   )

A．

1,-1

B．

2,-2

C．

1,-2

D．

2,-1