Here's some code to get you started. Note that I've included a reference to 'chbx_yes2', but the corresponding checkbox lacks the bookmark name.
Code:
Sub OnExitCB1B()
With ActiveDocument
Select Case .FormFields("drop_list").Result
Case "A"
.FormFields("Text1").Result = "xxx"
With .FormFields("Dropdown_yes_no")
.DropDown.Value = .DropDown.Default
.Enabled = False
End With
With .FormFields("chbx_yes2")
.CheckBox.Value = False
.Enabled = False
End With
With .FormFields("chbx_no2")
.CheckBox.Value = False
.Enabled = False
End With
Case "B"
.FormFields("Dropdown_yes_no").Enabled = True
.FormFields("chbx_yes2").Enabled = True
.FormFields("chbx_no2").Enabled = True
Case "C"
.FormFields("Dropdown_yes_no").Enabled = True
.FormFields("chbx_yes2").Enabled = True
.FormFields("chbx_no2").Enabled = True
End Select
End With
End Sub