Remove Value when Checkbox is unchecked

im trying to remove a value when a checkbox is unchecked. My Code:

var words = new List<string>();

if (ckbAnswer1.Checked)
   words.Add(" -A,");

if (ckbAnswer2.Checked)
   words.Add("B,");

if (ckbAnswer3.Checked)
   words.Add("C");

treeView1.SelectedNode.Text +=   treeView1.SelectedNode.Text +string.Join(" ", words);

Return Question 1 - A,B,C, but, say i want to uncheck "A", which should remove it from Question 1 - A,B,C. How do i do that?