<?php
$arr = file("word/healthy.txt");
mt_srand((double)microtime()*1000000);
print $arr[mt_rand(0,count($arr)-1)];
?><?php
$arr = file("word/diet.txt");
mt_srand((double)microtime()*1000000);
print $arr[mt_rand(0,count($arr)-1)];
?>が基本