Select each line that is correct and insert a Plain Text Content Control around it. You don't want the "- correct" text in your example.
Then run this macro. I've set it up to toggle so running it alternates showing or hiding the correct answers.
Code:
Sub ToggleAnswers()
Dim aCC As ContentControl, iColor As Long, iShowCC As Integer
If ActiveDocument.ContentControls(1).Range.Font.ColorIndex = wdBlack Then
iColor = wdGreen
iShowCC = wdContentControlBoundingBox
Else
iColor = wdBlack
iShowCC = wdContentControlHidden
End If
For Each aCC In ActiveDocument.ContentControls
With aCC.Range.Paragraphs(1).Range.Font
.ColorIndex = iColor
.Bold = .ColorIndex = wdGreen
aCC.Appearance = iShowCC
End With
Next aCC
End Sub