During runtime checkbox can be selected, if a checkbox is already selected or not by using the . . . . . . . . property.

The correct answer is: A. Checked

The Checked property of a checkbox indicates whether the checkbox is checked or not. It is a Boolean property, which means it can have either the value true or false.

The Unchecked property is not used to determine whether a checkbox is checked or not. It is used to set the checkbox to the unchecked state.

The On property is not used to determine whether a checkbox is checked or not. It is used to set the checkbox to the on state.

The Selected property is not used to determine whether a checkbox is checked or not. It is used to set the checkbox to the selected state.

Here is an example of how to use the Checked property to determine whether a checkbox is checked or not:

if (checkbox.Checked) {
// The checkbox is checked.
} else {
// The checkbox is not checked.
}