The correct answer is: A. opacity
The opacity property sets the opacity of an element. Opacity is a value between 0 and 1, where 0 is fully transparent and 1 is fully opaque.
The transparency property is deprecated and should not be used. It is equivalent to the opacity property with a value of 1.
The transparent keyword is a shorthand property for the opacity property with a value of 0.
Here is an example of how to use the opacity property:
css
div {
opacity: 0.5;
}
This will make the div element half transparent.