Which numbered sentence is the topic sentence?
(1) Sometimes, on thundery nights, young puppies become scared. (2) All that rumbling and rattling of windows is more than they can handle. (3) Even hidden beneath a blanket, they can still hear the thunder. (4) It definitely takes more than soft music to calm these animals. (5) I guess the only thundery time they are not afraid is when they are comforted by their owner.