1. I think the comma before the conjunction "or" is placed for emphasis (to emphasize the part "refund your money).<br/><br/>We are willing to exchange your shirts, or refund your money, whichever you prefer.<br/><br/>2. I don't know whether the comma before the conjunction "and" is placed to avoid confusion or for emphasis. Help.<br/><br/>According to the Collins COBUILD Advanced Learner's English Dictionary, the definition for the word "humid" is this.<br/><br/>You use <b>humid</b> to describe an atmosphere or climate that is very damp, and usually very hot.