Write a PHP program to check if a given string begins with 'abc' or 'xyz'. If the string begins with 'abc' or 'xyz' return 'abc' or 'xyz' otherwise

<?php
function test($s1)
{ 
      if (substr($s1,0,3) == "abc")
            {
                return "abc";
            }
            else if (substr($s1,0,3) == "xyz")
            {
                return "xyz";
            }
            else
            {
                return "";
            }
    }

echo test("abc")."\n";
echo test("abcdef")."\n";
echo test("C")."\n";
echo test("xyz")."\n";
echo test("xyzsder")."\n";