DIV和BODY的滚过条问题

如果让鼠标在DIV上滚动，当DIV滚动到最底，外边的滚动条，不能自己滚动，鼠标离开DIV的时候，外边(body)的滚动条才可以滚动<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>无标题文档</title>
</head><body>
<p>asdfjdsfdsfjdsfdsfsdfds</p>
<div style="width:500px; height:100px; overflow:auto" id="abc"> 
  <p>ds
    fds
    f
    sdf
    sdf
    sda
    fsd
    af
    sdaf
    sda
    fs
    dadf</p>
  <p>d</p>
  <p>fds</p>
  <p>f</p>
  <p>dsf</p>
  <p>dsf</p>
  <p>ds</p>
  <p>fdsf
    sda
    fsda
    f
    sdaf
    sda
    fsda
    fs
    dafsdafsdaf
    sdf
    sd
    f
    dsf
    dsf </p>
</div>
<p>&nbsp;</p>
<p>fds</p>
<p>f</p>
<p>sdaf</p>
<p>sdaf</p>
<p>sda</p>
<p>f</p>
<p>dsf</p>
<p>sd</p>
<p>fsda</p>
<p>f</p>
<p>sdf</p>
<p>sda</p>
<p>f</p>
<p>dsaf</p>
<p>sda</p>
<p>fds</p>
<p>f</p>
<p>sdf</p>
<p>sd</p>
<p>fds</p>
<p>f</p>
<p>dsf</p>
<p>ds</p>
<p>fds</p>
<p>f </p>
</body>
</html>