下列方程组是二元一次方程组的是（   ）

A：$\{\begin{array}{l}x-y=1\\ xy=2\end{array}$

B：$\{\begin{array}{l}4x-y=-1\\ y=2x+3\end{array}$

C：$\{\begin{array}{l}{x}^2-x-2=0\\ y=x+1\end{array}$

D：$\left\{\begin{array}{c}x-2y=3\\ \frac{1}{x}=6\end{array}\right.$