I do not see the complete code you wrote, but I have two ideas to try:
1. Use
return ddlanswer.Text;
in the ptoperty getter. SelectedText means the text portion selected in the "text editor" and not the item selected.
2. Use
ddlanswer.SelectedItem = value;
in the property setter. I guess you initialized the combo box with a set of strings, so you do not have a SelectedValue (that is a specified property of the selected item).