He did as much as he _____ her.
A.could help
B.could to help
C.helped
D.helping
答案:B
右心衰竭时呼吸困难的机制,主要为()
A.迷走神经兴奋性增高
B.心肌供血减少
C.右心房及上腔静脉压力升高
D.下肢静脉回流增多
E.肺淤血
正常颈外动脉血流频谱特点是()
A.低阻力频谱
B.高阻力频谱
C.三相或四相波
D.宽频毛刺样
E.宽频三峰递减型频谱