买甲、乙两种纯净水共用250元，其中甲种水每桶8元，乙种水每桶6元，乙种水的桶数是甲种水的桶数的75%，设买甲种水x桶，乙种水y桶，则所列方程组中正确的是      (       )

A：$\left\{\begin{array}{c}6x+8y=250\\ x=75\%y\end{array}\right.$

B：$\left\{\begin{array}{c}8x+6y=250\\ y=75\%x\end{array}\right.$

C：$\left\{\begin{array}{c}8x+6y=250\\ x=75\%y\end{array}\right.$

D：$\left\{\begin{array}{c}6x+8y=250\\ y=75\%x\end{array}\right.$