function change1(){
document.getElementById("features").style.display="block";
document.getElementById("spec").style.display="none";
document.getElementById("option").style.display="none";
}
function change2(){
document.getElementById("features").style.display="none";
document.getElementById("spec").style.display="block";
document.getElementById("option").style.display="none";
}
function change3(){
document.getElementById("features").style.display="none";
document.getElementById("spec").style.display="none";
document.getElementById("option").style.display="block";
}