There is            rain and it's             cool this summer. [ ]

A. much too, too much

B. much too, much too

C. too much, much too

D. too much, too much

正常肺静脉血流的多普勒频谱有什么特点（）。

A.收缩期、舒张期各有一负向的峰

B.只有舒张期一个正向的尖峰波

C.收缩期、舒张期各有一正向的峰，后者大于前者

D.舒张期呈双峰、均正向

E.收缩期呈双峰，均为负向，无舒张期血流