下列方程组中是二元一次方程组的是（　　）

A：$\left\{\begin{array}{c}x-y=3\\ xy=1\end{array}\right.$

B：$\left\{\begin{array}{c}2x+y=5\\ x=3y-2\end{array}\right.$

C：$\left\{\begin{array}{c}{x}^2-y=1\\ y=2x\end{array}\right.$

D：$\left\{\begin{array}{c}\frac{1}{y}-x=2\\ x+y=0\end{array}\right.$