下列物质中属于离子化合物的是[ ]
A．苛性钾
B．碘化氢
C．硫酸
D．醋酸
答案：A
When the thief found the police had already __________ him, he ran away quickly.[ ]
A. realized
B. known
C. spotted
D. stared
图示某半开的阀门，阀门前后测压管水头差△h=1m水柱，管径不变，管中平均流速v=2m/s，则该阀门的局部阻力系数ζ为（）。
A．4.9
B．6.1
C．3.4
D．4.2
