In most parts of the world, the hand gesture of connecting the index finger with the thumb to create a circle signifies "okay" (or "OK" or "a-OK"). So, your best answer would be "A," although under some circumstances, it could also signify your approval over a person's looks ("B") or the quality taste of food ("C"). However, in some parts of the world, particularly Southern Europe (which could include Italy) and South America, it can be interpreted as an offensive sign. Italians also use the OK sign with both hands to signify "perfetto" or "perfection."
I assume that you are asking this in the context of cross-cultural communications. Gestures like this are something that a person has to be very careful about because they can mean one thing in the person's own country and something entirely different abroad.
In the US, the sign you describe means "OK." However, in Italy, as in many other countries, it means something else. Of the options you have given, the right answer is "D." As I understand it, "worthless" is actually a polite way of saying what this gesture means. It is said to mean the same thing as showing someone the middle finger in the US.