Are you going to watch TV _____________ Saturday evening?[ ]

A. at

B. in

C. on

正常情况下，如将频谱多普勒舒张期取样容积位于二尖瓣上左房腔内可观察到

A．负向双峰频谱

B．形态与二尖瓣口血流频谱相差较大

C．E/A比值常≤1

D．频谱幅度高于二尖瓣口血流

E．E/A比值常≥1