21.( ) 執行下列Visual Basic程式片段後，A(0)-A(5)的值為何？ Dim a(5), i , b As Integer a(0) = 27 : a(1) = 12 : a(2) = 8 a(3) = 9 : a(4) = 21 : a(5) = 72 For i = 0 To 2 　　b = a(i) 　　a(i) = a(5 - i) 　　a(5 - i) = b Next i (A)27,12,8,9,21,72 (B)72,27,21,12,9,8 (C)72,21,9,8,12,27 (D)8,9,12,21,27,72。