下列哪一项不是视网膜母细胞瘤的超声表现（）。

A.眼内实性肿物

B.瘤组织内钙斑反射

C.肿物有后运动

D.高速、高阻型动脉频谱

E.肿物内可见与视网膜中央动、静脉相连续的血流频谱

The constitution, unlike other forms of laws, is fundamental ______ our social system working properly. [ ]

A. for keeping  

B. to keeping  

C. to keep    

D. with keeping