畸胎瘤特征性的X线征象是:()
A.肿瘤位于前纵隔
B.肿瘤呈圆形、卵圆形或分叶状
C.肿瘤内有密度减低区
D.肿瘤内有骨影或牙齿影
E.肿瘤边缘呈锯齿状或毛刺状
参考答案:D
23.______ is reported, a new town has been built on the ruins left by the big earthquake.
A.It
B.As
C.Which
D.This
在Visual FoxPro中,主索引可以保证数据的()完整性。