有如下VB 程序段：

i = 0: s = "": n = 0

Do While i <= 3

    k = i: j = i + 1

    Do While j <= 7

        If a(j) < a(k) Then k = j

        j = j + 1

    Loop

    If i <> k Then

        t = a(i): a(i) = a(k): a(k) = t

        n = n + 1

    End If

    s = s + Str(a(i)): i = i + 1

Loop

Label1.Caption = Str(n) + ":" + s

数组a(0)到a(7)依次为16, 19, 8, 20, 4, 12,6, 15，程序运行后，标签框Label1中显示的值为（   ）

A、3:4 6 8

B、4:4 6 8

C、3:4 6 8 12

D、4:4 6 8 12