He never gave up, _____ he failed many times.[ ]
A. and
B. though
C. or
D. but
答案:B
风湿性心脏病最常见的瓣膜病变是()
A.二尖瓣狭窄
B.二尖瓣关闭不全
C.三尖瓣狭窄
D.主动脉瓣狭窄
E.主动脉瓣关闭不全
CT值的定义是以()的衰减系数为标准来计算各种组织的CT值
A.空气
B.骨
C.水
D.脑组织
E.以上都不是