You're talking about an apparently gratuitous gesture. Well, if you give a gratuity to a waiter, you're doing it freely; you don't have to, it's not necessarily earned. It talks about an apparently gratuitous gesture, whether or not it arouses our suspicion, while a gesture recognized to be _______ gives no reason for surprise. Well, to contrast with gratuitous would be warranted because warranted is something that is earned. So, A is the correct answer.