根据短文，选择正确答案。

     My name is Zhou Dan. I'm a Chinese girl. I'm twelve. I'm from Zhengzhou, China. Do you know Zhengzhou? It's in the middle of China. I'm in No. 8 Middle School. There are about nine hundred students and fifty teachers in our school. Ours is a good school in Zhengzhou. I'm in Class 2, Grade 1. There are 49 students in our class, 29 girls and 20 boys. My English teacher is Miss Zhao Dan. Our names are almost the same, right? She is nice to me. We're good friends. I like English, and I like music, too. I want to find a pen friend. Please write to me.

已知直线y=2x与y=﹣x+b的交点为（﹣1，a），则方程组 $\left\{\begin{array}{c}y-2x=0\\ y+x-b=0\end{array}\right.$的解为（　　）

西周时期的王位世袭制与夏商时期相比，最突出的特点是（     ）