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Which of the following methods is called to directly echo or print() an object?

__unset()

__isset()

__toString()

__set_state()

Explanation: Answer option C is correct.

The __toString() method is called to directly echo or print() an object. It allows a programmer to set a string value for the object that will be used if the object is ever used as a string. The example of the __toString() magic method is as follows:

<?php
 class boy {
 public function __toString() {
 return "This is a boy\n";
 }
 }
 $toby = new boy;
 print $toby;
?>

Answer option D is incorrect. The __set_state() magic method is inserted dynamically by var_export() to allow for reinitialization on the execution of var_export()'s output.

Answer option A is incorrect. The __unset() method is called when an undefined property is passed to unset().

Answer option B is incorrect. The __isset() method is called when an undefined property is passed to isset().

Reference: http://php.net/manual/en/language.oop5.magic.php