Answer :
Choice A. The word, "whistles"is the subject. Whistles is plural. This tells you that you need a singular verb. Whenever you have a plural subject, replace it with "they."
Whistles dangle. = They dangle.
Whistles dangle. = They dangle.
Well, B. is so not the choice. It would be C because it is plural due to the 'two silver whistles'. Hope this helped!