设实数$x,y$满足约束条件$\{\begin{array}{c}x\ge 0\\ x+2y\ge 3\\ 2x+y\le 3\end{array}$，则$z=x-y$的最小值为 (   )

    Mary is an English girl, but she lives(居住) in China. She is six. Her mother says to her, “You are six now, Mary, you are going to school. I think it is very good. It's a nice school.”

    “Is it a Chinese school?” Mary asks.

    “Yes, it is.” Her mother says.

    It is September and the new school year begins. Mary goes to school every day. She likes her lessons and her classmates(同学)very much. Her classmates like her, too. She always gets good grades(成绩) in math, so she often helps her friends with math. Mary thinks Chinese is too difficult, so she can't speak Chinese very well. But she likes the people of China and Chinese food very much.

根据短文内容，判断下列句子的正误。

下列说法正确的是（　　）

（Ⅰ）求点P的轨迹C的方程；

（Ⅱ）若点M，N是直线l₁上两个不同的点，且△PMN的内切圆方程为x²+y²=1，直线PF的斜率为k，求 $\frac{\left|K\right|}{\left|MN\right|}$ 的取值范围．