For Each / Next

I need some help using for each / next, as I am not very familiar with how to use it. I have a worksheet with many combo boxes. I want to ensure that all of these drop downs have an answer before being emailed back to me for review. I was thinking something along these lines...

Dim Question As ComboBox
Dim Question As String
Dim WS As Worksheet

For Each WS In Worksheets (do not know what i need here)
If Question = "" Then
Msg = MsgBox("All questions have not been completed. Please double-check the drop down boxes to ensure no questions were left unanswered.", vbOKOnly, "Missing Answers")
End If
Next Question

Can anyone help me?

Thank you,

NicB.