When someone phones you in a business scene, if you don't know what the person is referring to,<br/>what is the best way to ask? If I say<br/><br/>1, What are you talking about ? Would it be rude?<br/><br/>2,What are you referring to? Would it sound ok?<br/><br/>3,What are you regarding? Would it sound ok?<br/><br/>I always say "Regarding what??". I think this is not suitable.<br/><br/>I would be grateful if someone could teach me.<br/><br/>Thanks