George. W. Bush, _______ President of the United States, is to visit China  _______ third time.

A．a；a

B．the；a

C．/；a

D．/；the

螺旋扫描中有关重建间隔的叙述，正确的是()

A.重建间隔与扫描层厚一致

B.重建间隔大于扫描层厚

C.重建间隔与螺距一致

D.重建间隔是相邻两横断面图像之间长轴方向上的距离

E.重建间隔由扫描长度决定