题目

One day Mrs. Wilson went shopping with Tracy and Ben. They went to the supermarket in the new shopping center.      Why do you buy things here? Tracy wanted to know. Because they are cheaper here than at the corner store near our home, Mrs. Wilson said. Help me check the prices, please.       The Wilsons were not rich and Mrs. Wilson was always careful with her money. She looked carefully after the prices of things. She bought lots of things in the supermarket. When they got home, the children said, We don't think you saved money by going to the supermarket.  Of course 设集合A＝{x|x2＋4x＝0，x∈R}，B＝{x|x2＋2(a＋1)x＋a2－1＝0，a∈R，x∈R}，若B⊆A，求实数a的取值范围．