private void checkAnswer(CheckedListBox clb, int ind)
{
if (clb.SelectedIndex != -1)
{
for (int i = 0; i < 4; i++)
{
if (i != clb.SelectedIndex && clb.GetItemChecked(i))
clb.SetItemChecked(i, false);
}
clb.ClearSelected();
}
}