What will be the output of the following PHP code? <?php $a1 = array("red", "green"); $a2 = array("blue", "yellow"); print_r(array_merge($a1, $a2)); ?>

• A. Array ( [0] =&gt; red [1] =&gt; green)
• B. Array ( [0] =&gt; blue [1] =&gt; yellow [2] =&gt; red [3] =&gt; green )
• C. Array ( [0] =&gt; red [1] =&gt; green [2] =&gt; blue [3] =&gt; yellow )
• D. Array ( [0] =&gt; blue [1] =&gt; yellow )