虾的那个部位有寄生虫:请问谁那有"每刷新次网页时可以改变图片"的代码??????????

<script language="JavaScript">
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today=new Date();
jran=today.getTime();
function rnd() {
ia=9301;
ic=49297;
im=233280;
jran = (jran*ia+ic) % im;
return jran/(im*1.0);
};
function rand(number) {
return Math.ceil(rnd()*number);
};
document.write("<CENTER>");
for(i=1;i<=1;i++) {
myNum=(rand(18));
if(myNum == 1) document.write("<img src='/images/sj/1.jpg'>");
if(myNum == 2) document.write("<img src='/images/sj/2.jpg'>");
if(myNum == 3) document.write("<img src='/images/sj/3.jpg'>");
if(myNum == 4) document.write("<img src='/images/sj/4.jpg'>");
if(myNum == 5) document.write("<img src='/images/sj/5.jpg'>");
if(myNum == 6) document.write("<img src='/images/sj/6.jpg'>");
if(myNum == 7) document.write("<img src='/images/sj/7.jpg'>");
if(myNum == 8) document.write("<img src='/images/sj/8.jpg'>");
if(myNum == 9) document.write("<img src='/images/sj/9.jpg'>");
if(myNum == 10) document.write("<img src='/images/sj/10.jpg'>");
if(myNum == 11) document.write("<img src='/images/sj/11.jpg'>");
if(myNum == 12) document.write("<img src='/images/sj/12.jpg'>");
if(myNum == 13) document.write("<img src='/images/sj/13.jpg'>");
if(myNum == 14) document.write("<img src='/images/sj/14.jpg'>");
if(myNum == 15) document.write("<img src='/images/sj/15.jpg'>");
if(myNum == 16) document.write("<img src='/images/sj/16.jpg'>");
if(myNum == 17) document.write("<img src='/images/sj/17.jpg'>");
if(myNum == 18) document.write("<img src='/images/sj/18.jpg'>");
else {
document.write();
}
};
document.write("</CENTER>");
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</script>