A:向氯化铁溶液中加入铜粉 Fe3++Cu===Fe2++Cu2+
B:硫酸铝溶液中滴入氨水 Al3++OH— =Al(OH)3↓
C:FeBr2溶液中滴加少量氯水 2Fe2++Cl2===2Fe3++2Cl—
D:将过量CO2通入偏铝酸钠溶液中 2AlO2-+CO2+3H2O=2Al(OH)3↓+CO32—
⑴Do you want some rice?____ A. Thanks.
⑵What do you want to drink?____ B. Yes, I do.
⑶Can I help you? ____ C. I want some bread.
⑷Here you are.____ D. Water, please.
⑸Do you want coffee or tea?____ E. I want some tea, please.
如图所示,一辆卡车后面用轻绳拖着质量为m的物体A,A与地面的摩擦不计.
函数f(x)=2cos2x-1-xx-1,其图象的对称中心是( )