Which numbered sentence is the topic sentence? (1) The first puppy born was white. Imagine that—white! (2) We had taken special care to breed this dog with a black poodle so that there would be no white dogs, but there it was, a white dog with paws tipped with black and a black splash right in the middle of his chest. (3) The second, third, fourth, fifth, and sixth, however, were just the opposite. (4) They were all black with white spots, especially on their faces and ears. (5) We could not believe that these puppies were from the same mother.