假设$a=range(1,20,5)，则print_r($a)的输出结果为（ ）。
A.
Array ( [0] => 1 [1] => 6 [2] => 11 [3] => 16 )
B.
Array ( [0] => 1 [1] => 20[2] => 5 )
C.
Array ( [0] => 5 [1] => 10 [2] => 15 [3] => 20 )
D.
Array ( [0] => 5 [1] => 10 [2] => 15 )
正确答案是A