Which expression is equivalent to the following complex fraction? startfraction 1 over x endfraction minus startfraction 1 over y endfraction divided by startfraction 1 over x endfraction + startfraction 1 over y endfraction startfraction y + x over y minus x endfraction startfraction (y minus x) (y + x) over x squared y squared endfraction startfraction x squared y squared over (y + x) (y + x) endfraction startfraction y minus x over y + x endfraction.