What will be the value of $a?

After performing the following operations:
<code>
$a = array(‘a’, ‘b’, ‘c’);
$a = array_keys(array_flip($a));
</code>
What will be the value of $a?

A.
array(‘c’, ‘b’, ‘a’)

B.
array(2, 1, 0)

C.
array(‘a’, ‘b’, ‘c’)

D.
None of the above