甲、乙两人同求方程ax-by=7的整数解，甲正确地求出一个解为x=1y=-1，乙把ax-by=7看成ax-by=1，求得一个解为x=1y=2，则a，b的值分别为(      )

A：$\left\{\begin{array}{c}a=2\\ b=5\end{array}\right.$­

B：$\left\{\begin{array}{c}a=5\\ b=2\end{array}\right.$­

C：$\left\{\begin{array}{c}a=3\\ b=5\end{array}\right.$­­

D：$\left\{\begin{array}{c}a=5\\ b=3\end{array}\right.$