以上程序段运行的结果是：______.
Dim a(-1 To 5) As Boolean
Dim flag As Boolean
flag = False
Dim i As Integer
Dim j As Integer
Do Until flag = True
For i = -1 To 5
j=j+1
if a(i)= False Then
a(i)= True
Exit For
End If
If i = 5 Then
flag = True
End If
Next
Loop
Print j

A．20

B．7

C．35

D．8

如何消除空压机冷却器内结垢？