— Must I make a choice among the five dictionaries right now?

—  __________, you don't have to decide immediately. [ ]

A. It makes no difference    

B. Just take your time      

C. Look at it slowly        

D. I don't care at all

彩色多普勒血流显像仪的伪彩功能的作用是（）。

A.增加彩色血流检出敏感度，增加低速血流的显示能力

B.增加彩色血流的信息量

C.增加灰阶图像的视觉分辨能力

D.能进行定量测量