<input type="button" id="b1" value="偶数行红色"><br>
<input type="button" id="b2" value="奇数行绿色"><br>
<table border=1 width="100px">
<tr><td>1</td><td>1</td><td>1</td><td>1</td></tr>
<tr><td>2</td><td>2</td><td>2</td><td>2</td></tr>
<tr><td>3</td><td>3</td><td>3</td><td>3</td></tr>
<tr><td>4</td><td>4</td><td>4</td><td>4</td></tr>
<tr><td>5</td><td>5</td><td>5</td><td>5</td></tr>
</table><br>
<input type="button" id="b3" value="奇数列红色"><br>
<input type="button" id="b4" value="偶数列绿色"><br>
<table border=1 width="100px">
<tr><td>1</td><td>1</td><td>1</td><td>1</td></tr>
<tr><td>2</td><td>2</td><td>2</td><td>2</td></tr>
<tr><td>3</td><td>3</td><td>3</td><td>3</td></tr>
<tr><td>4</td><td>4</td><td>4</td><td>4</td></tr>
<tr><td>5</td><td>5</td><td>5</td><td>5</td></tr>
</table><br>
<input type="button" id="b5" value="奇数元素绿色"><br>
<table border=1 width="100px">
<tr><td>1</td><td>1</td><td>1</td><td>1</td><td>1</td></tr>
<tr><td>2</td><td>2</td><td>2</td><td>2</td><td>2</td></tr>
<tr><td>3</td><td>3</td><td>3</td><td>3</td><td>3</td></tr>
<tr><td>4</td><td>4</td><td>4</td><td>4</td><td>4</td></tr>
<tr><td>5</td><td>5</td><td>5</td><td>5</td><td>5</td></tr>
</table>

$('#b1').click(function(){
/*table:eq(0) tr:even table:eq(0):筛选出第一张表格 tr:even:筛选出tr属性的对象
*注意table和tr对象中间有空格，表示从属关系
*/
$('table:eq(0) tr:even').css("background","red"); 
});
$('#b2').click(function(){
$('table:eq(0) tr:odd').css("background","green");
});
$('#b3').click(function(){
$('table:eq(1) td:even').css("background","red");
});
$('#b4').click(function(){
$('table:eq(1) td:odd').css("background","green");
});
$('#b5').click(function(){
$('table:eq(2) td:even').css("background","green");
});