--- Where is your mother?

--- She _______ to Sichuan on business. She has ______ there four times recently.

A．has gone, gone

B．has been, been

C．has gone, been

D．has been, gone

下列物质分离方法错误的是[ ]

A．粗盐提纯的步骤：溶解→过滤→蒸发结晶

B．除去CO₂中混有少量的CO：导出点燃

C．除去H₂中混有的HCl：将气体通过装有NaOH溶液的洗气瓶

D．除去铜粉中混有的CuO：用足量的稀硫酸浸泡后过滤、洗涤