Answer: Option A and Option D
Step-by-step explanation:
By definition the general equation of a circle has the following form

Where r is the radius and the point (h, k) is the center of the circle
All points that are on the x axis have the following form:
(h, 0)
Therefore all the circles that have their centers on the x axis will have a value of k = 0.
Identify among the options all those equations that have a value of k = 0
The circles that have their center on the x axis are option A and option D