The correct answer is (b) fadeOn()
For explanation I would say: jQuery has various fade methods including fadeout(), fadeTo(), fadeToggle(), fadeIn().
The syntax of fadeIn() is $(selector).fadeIn(speed,callback);
For fadeout() we use $(selector).fadeOut(speed,callback);
For fadeToggle we use $(slecetor).fadeToggle(speed,callback);
For fadeTo() syntax is $(selector).fadeTo(speed,opacity,callback).