四肢血管正常的多普勒频谱波形是()。
A.单相波
B.双相波和单相波
C.双相波
D.三相波
E.单相波和三相波
参考答案:D
解析:四肢血管正常的多普勒频谱波形是三相波。
--- Why do you often take exercise? --- _____ me keep fit.
A.Help
B.Helping
C.To help
D.helped
In the early morning, all of us stood at the top of the mountain to ________ east of the city, watching ________ burning sun rising.
A.the; a
B./; a
C.the; the
D.the;/