脊髓灰质炎的病理变化主要在（）
A.脊髓胸段
B.脊髓颈段和腰段
C.脑神经运动神经核
D.脊髓颈段
E.脊髓椎体传导束
参考答案：B
若am=2，bn=4，则a2mb-2n=______．
—Hurry up! It's the very time we ______ to school.
—Wait for me![ ]
A. have gone
B. could go
C. went
D. go
