脊髓内肿瘤的MRI表现为
A.患侧蛛网膜下隙增宽B.患侧蛛网膜下隙受压变窄C.蛛网膜下隙对称性变窄D.蛛网膜下隙对称性增宽E.健侧蛛网膜下增宽
参考答案:C
—Do you know the boy under the tree?
—Yes, I know. He is creative and imaginative, but he is a little lazy ______. [ ]
A. once a time
B. at a time
C. at times
D. at time
完全竞争市场的局限?