Which of the following CSS Property defines the x-coordinate of the background-position property?

The correct answer is A. background-position-x.

The background-position property defines the initial position of a background image. It takes two values, which represent the horizontal and vertical position of the image, respectively. The horizontal position is defined by the background-position-x property, and the vertical position is defined by the background-position-y property.

For example, the following CSS code will position a background image 10px to the right and 20px from the top of the element:

css
background-position: 10px 20px;

The background-x-axis and background-y-axis properties are not valid CSS properties.