Hello,<br/><br/>Which of the following is the appropriate response when a sales lady in a store approaches you and says "Do you need any help?"?<br/><br/>A. No, <b>I'm</b> fine.<br/>B. No, <b>it's</b> fine.<br/>C. No, <b>that's</b> fine.<br/><br/>I understand this seems to be a very simple question, but I'd just like to hear what native speakers say in such a situation. Thank you in advance.<br/><br/>By the way, is there a difference in meaning between saying <b>'it's fine'</b> and <b>'that's fine'</b>? When is one appropriate instead of the other?