A.var btn = $('#btn');
btn.mouseover(function(){
btn.css('background-color','yellow');
});
btn.mouseout(function(){
btn.css('background-color','white');
});
B.var btn = $('#btn');
btn.mousein(function(){
btn.css('background-color','yellow');
});
btn.mouseout(function(){
btn.css('background-color','white');
});
C.var btn = $('#btn');
btn.mouseover(function(){
btn.css('background-color','yellow');
});
btn.mouseleave(function(){
btn.css('background-color','white');
});
D.var btn = $('#btn');
btn.mouseover(function(){
btn.css('color','yellow');
});
btn.mouseout(function(){
btn.css('color','white');
});