小秦用VB编写十进制数自动转换成二进制数的程序,运行界面如下图,运行代码如下:

Private Sub Command1_Click()
Dim a, i, n As Integer,s as string
n = Val(Text1.Text)
Do While n > 0
① ② ③ Loop
Text2.Text = s
End Sub
缺少部分的代码应填( )。
A.①a = n Mod 2 ②n = n \ 2 ③ s = Str(a) + s |
B.①n = n \ 2 ②a = n Mod 2 ③ s = Str(a) + s |
C.①a = n Mod 2 ②n = n \ 2 ③ s = s +Str(a) |
D.①n = n \ 2 ②a = n Mod 2 ③ s = s +Str(a) |