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.
}