溃疡型胃癌的典型声像图特征是（）。
A.短轴图像上可见多环"同心圆征"
B."火山口征"
C."腊肠征"
D."假肾征"
E."鱼刺征"
参考答案：B
— Did Peter fix the computer himself?
— He _____, because he doesn't know much about computers. [ ]
A. has it fixed
B. had fixed it
C. had it fixed
D. fixed it
一个原子核进行一次α衰变后成为，然后又进行了一次β衰变，成为，它们的质量数a、c、f及核电荷数b、d、g之间应有的关系是[ ]
A．a = f + 2
B．c = f
C．d = g一1
D．b = g－1
进行一次α衰变后成为
，然后又进行了一次β衰变，成为
，它们的质量数a、c、f及核电荷数b、d、g之间应有的关系是[ ]