题目在下列方程组中,是二元一次方程组的是（ ）A.{x+2y=zx−3y=3\left\{\begin{array}{l}x+2y=z\\ x-3y=3\end{array}\right.{x+2y=zx−3y=3B.{x=−1y=x+3\left\{\begin{array}{l}x=-1\\ y=x+3\end{array}\right.{x=−1y=x+3C.{xy=3x−y=4\left\{\begin{array}{l}xy=3\\ x-y=4\end{array}\right.{xy=3x−y=4D.{1x+y=0x+2y=3\left\{\begin{array}{l}\frac{1}{x+y}=0\\ x+2y=3\end{array}\right.{x+y1=0x+2y=3知识点：解二元一次方程组——代入消元法章节：方程与不等式 / 二元一次方程组
