.htaccess中设立 RewriteCond %{HTTP_HOST} 不起作用

.htaccess中设置 RewriteCond %{HTTP_HOST} 不起作用
RewriteEngine on
RewriteCond %{HTTP_HOST} ^aaa$ [NC]
RewriteRule ^([a-zA-Z]+/)+list-([0-9]+)-([0-9]+).html index.php?m=content&c=index&a=lists&catid=$2&page=$3
RewriteRule ^([a-zA-Z]+/)+show-([0-9]+)-([0-9]+)-([0-9]+).html index.php?m=content&c=index&a=show&catid=$2&id=$3&page=$4
RewriteCond %{HTTP_HOST} ^bbb$ [NC]
RewriteRule ^([a-zA-Z]+/)+list-([0-9]+)-([0-9]+).html index.php?m=wap&c=index&a=lists&catid=$2&page=$3
RewriteRule ^([a-zA-Z]+/)+show-([0-9]+)-([0-9]+)-([0-9]+).html index.php?m=wap&c=index&a=show&catid=$2&id=$3&page=$4


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bbb是个手机站，地址跟aaa是不一样的
这样设置之后，访问bbb还是使用aaa的规则，RewriteCond %{HTTP_HOST}没起作用呀，麻烦帮俺看看，谢谢。
------解决思路----------------------
RewriteEngine on
RewriteCond %{HTTP_HOST} ^aaa$
RewriteRule ^([a-zA-Z]+/)+list-([0-9]+)-([0-9]+).html index.php?m=content&c=index&a=lists&catid=$2&page=$3 [NC]
RewriteRule ^([a-zA-Z]+/)+show-([0-9]+)-([0-9]+)-([0-9]+).html index.php?m=content&c=index&a=show&catid=$2&id=$3&page=$4 [NC]

RewriteCond %{HTTP_HOST} ^bbb$
RewriteRule ^([a-zA-Z]+/)+list-([0-9]+)-([0-9]+).html index.php?m=wap&c=index&a=lists&catid=$2&page=$3 [NC]
RewriteRule ^([a-zA-Z]+/)+show-([0-9]+)-([0-9]+)-([0-9]+).html index.php?m=wap&c=index&a=show&catid=$2&id=$3&page=$4 [NC]