已知变量x,y满足约束条件$\left\{\begin{array}{c}\begin{array}{c}y+x-1\le 0\\ y-3x-1\le 0\\ y-x+1\ge 0\end{array}\\ \end{array}\right.$则z=2x+y的最大值为 （     ）

⑴plant vegetables ____          A. in the park

⑵watch a film ____              B. at the zoo

⑶have dinner ____              C. at the cinema

⑷watch animals ____            D. on the farm

⑸fly a kite ____                  E. in the restaurant