The correct answer is: A. Checked
The Checked property of a radio button indicates whether the radio button is selected or not. If the Checked property is set to true, the radio button is selected. If the Checked property is set to false, the radio button is not selected.
The Unchecked property is not used to determine whether a radio button is selected or not. The Unchecked property is used to set the initial state of a radio button. If the Unchecked property is set to true, the radio button is not selected when the form is loaded. If the Unchecked property is set to false, the radio button is selected when the form is loaded.
The On property is not used to determine whether a radio button is selected or not. The On property is used to specify the event that will be raised when the radio button is clicked.
The Selected property is not used to determine whether a radio button is selected or not. The Selected property is used to get or set the value of the radio button. The Selected property is a Boolean value that indicates whether the radio button is selected.
Here is an example of how to use the Checked property to determine whether a radio button is selected:
private void button1_Click(object sender, EventArgs e)
{
if (radioButton1.Checked)
{
// The radio button is selected.
}
else
{
// The radio button is not selected.
}
}