单项选择题

运行下列程序,输入数据8、9、3、0后,窗体中显示的结果是______。
Private Sub Form_click()
Dim sum As Integer,m As Integer
sum=0
Do
m=InputBox("输入m")
sum=sum+m
Loop Until m=0
MsgBox sum
End Sub

A.0
B.17
C.20
D.21