在进行多普勒检查时哪项不需特别关注（）
A.血流方向
B.血流信号的特征
C.有无血流
D.多普勒增益
E.利用彩色多普勒测量血管宽度
参考答案：E
Doctors _____ in every part of the world now.[ ]
A. are needing
B. are needed
C. were needing
D. were needed
叙述产生静息电位的离子机制。
