代码有问题，求解

Question

<?php
echo _FILE_;
echo "<br />";
echo _LINE_;
echo "<br />";
echo PHP_VERSION;
echo "<br />";
echo PHP_OS;
echo "<br />";
?>

Answer 1

下划线是两个

Answer 2

下划线应该是两个

Answer 3

<?php echo __FILE__; echo "<br />"; echo __LINE__; echo "<br />"; echo PHP_VERSION; echo "<br />"; echo PHP_OS; echo "<br />"; ?>