— _ backpack is this?
—I think it belongs to my sister. [ ]
A. Who's
B. Whose
C. Who
答案:B
盛有12mL NO2和O2的混合气体的量筒倒立于水槽中,充分反应后,还剩余2mL无色气体,则原混合气体中O2的体积是( )
A.1.2mL
B.2.4mL
C.3.6mL
D.4.8mL
简述离心式泵与风机的工作原理。