<select name =s1>
<option value=a1>a1</option>
<option value=a2>a2</option>
<option value=a3>a3</option>
</select>
<select name =s2 onchange="ta.value+=s1.value+' '+s2.value+'\n'" >
<option value=b1>b1</option>
<option value=b2>b2</option>
</select>
<textarea name =ta></textarea>
<option value=a1>a1</option>
<option value=a2>a2</option>
<option value=a3>a3</option>
</select>
<select name =s2 onchange="ta.value+=s1.value+' '+s2.value+'\n'" >
<option value=b1>b1</option>
<option value=b2>b2</option>
</select>
<textarea name =ta></textarea>
<select name =s1>
<option value=a1>a1</option>
<option value=a2>a2</option>
<option value=a3>a3</option>
</select>
<select name =s2 onchange="document.frm.ta.value+=document.frm.s1.value+' '+document.frm.s2.value+'\n'" >
<option value=b1>b1</option>
<option value=b2>b2</option>
</select>
<textarea name =ta></textarea>
</form>加个表单试试。