function seleciona_comprar() {
   var spanAlugar = document.getElementsByClassName("spanRent");
   for (i = 0; i < spanAlugar.length; ++i) {
     spanAlugar[i].style.display = "none";
   }
   var spanComprar = document.getElementsByClassName("spanBuy");
   for (i = 0; i < spanComprar.length; ++i) {
     spanComprar[i].style.display = "inline";
   }
}

function seleciona_alugar() {
   var spanComprar = document.getElementsByClassName("spanBuy");
   for (i = 0; i < spanComprar.length; ++i) {
     spanComprar[i].style.display = "none";
   }
   var spanAlugar = document.getElementsByClassName("spanRent");
   for (i = 0; i < spanAlugar.length; ++i) {
     spanAlugar[i].style.display = "inline";
   }
}