This boy is Peter Smith. His1 name is Peter. His2 name is Smith. This is3 school. His school4number is 20048567. His teacher is Miss White. Miss White 5a good teacher. Li Min is a Chinese boy. Li Min is his good 6 at school. Look!7 a pencil sharpener. Is the pencil sharpener 8? I9know. Let's10 Li Min at 495-6548.

我国西北地区物资出口最为便捷的铁路是(       )

已知a+b=4，a﹣b=3，则a²﹣b²=（　　）