#head {
  background: url(../images/back1.jpg) no-repeat top left #000000;
}
#head.a { background: url(../images/back1.jpg) no-repeat top left #000000; }
#head.b { background: url(../images/back2.jpg) no-repeat top left #000000; }
#head.c { background: url(../images/back3.jpg) no-repeat top left #000000; }
#head.d { background: url(../images/back4.jpg) no-repeat top left #000000; }
#head.e { background: url(../images/back5.jpg) no-repeat top left #000000; }