A. A sudden decrease in abdominal pain is a classic sign of appendiceal rupture or perforation. The pain often decreases after perforation due to the release of pressure from the appendix, but it can worsen once peritonitis develops. B. A low-grade fever may be present in appendicitis, but it is not a specific indicator of perforation. Fever is more commonly associated with infection or inflammation. C. Rovsing's sign refers to referred pain in the lower right quadrant when the left side of the abdomen is palpated, and it is present in many cases of appendicitis. Its absence is not a reliable indicator of perforation. D. A flaccid abdomen is more suggestive of peritonitis, which can occur after perforation. However, a sudden decrease in pain is a stronger sign of perforation.