#site-box {
          width : 1000px;
          margin-right: auto;
          margin-left : auto;
}

p {
          margin-left: auto
          margin-right: auto
          padding: 20px;
}


#a-box {    }

#b-box {
          float: left;
          width: 500px;
}

#c-box {
          float: right;
          width: 250px;
}

#d-box {    }