下列标志不正确的是（　　）
               

读一读，把正确答案代码填入相应的括号里。

① What can you do?____      A. I need a new dress.

② What can she do?____      B. I can ride a bicycle.

③ What can he do?____       C. She can fly a kite.

④ What do you need?____   D. He can play football.

三元一次方程组$\left\{\begin{array}{c}x-y=-1\\ y-z=-1\\ x+z=4\end{array}\right.$的解是____