二次函数y=x2-2x的对称轴是______．
根据题意得x=-b2a=--22×1=1．
即对称轴是x=1．
The discussion was held in a lively______ with members talking freely to each other．
A．atmosphere
B．weather
C．situation
D．phenomenon
在食醋中可以大量存在的离子是[ ]
A．HCO3-
B．CO32-
C．OH－
D．Cl－
