Given the task definition, example input & output, solve the new input case.
Given a context passage, generate a question from the passage such that its answer is shortest continous span from the passage.
Example: In 1582 the united provinces invited francis, duke of anjou to lead them; but after a failed attempt to take antwerp in 1583, the duke left the netherlands again. after the assassination of william of orange (10 july 1584), both henry iii of france and elizabeth i of england declined the offer of sovereignty. however, the latter agreed to turn the united provinces into a protectorate of england (treaty of nonsuch, 1585), and sent the earl of leicester as governor-general. this was unsuccessful and in 1588 the provinces became a confederacy. the union of utrecht is regarded as the foundation of the republic of the seven united provinces, which was not recognized by the spanish empire until the peace of westphalia in 1648.
Output: In what year did francis, duke of anjou leave the netherlands?
The generated question is perfect. Because the question is based on second sentence of the input passage and its answer is 1583.

New input case for you: A blinded, retrospective study was performed to determine the value of supine abdominal radiographs in diagnosing pneumoperitoneum. Supine films from 44 cases of pneumoperitoneum were randomly interspersed among supine films from 87 control subjects without free air, and the films were reviewed for the presence or absence of various signs of pneumoperitoneum, including Rigler's sign (gas on both sides of the bowel wall), the falciform ligament sign (gas outlining the falciform ligament), the football sign (gas outlining the peritoneal cavity), the inverted-V sign (gas outlining the medial umbilical folds), and the right-upper-quadrant gas sign (localized gas in the right upper quadrant). One or more of these signs were present in 26 cases (59%) of pneumoperitoneum, including the right-upper-quadrant gas sign in 18 cases (41%), Rigler's sign in 14 cases (32%), and the falciform ligament and football signs in one case each (2%). Unfortunately, there were frequent errors in the interpretation of the right-upper-quadrant gas sign and Rigler's sign, with a total of 11 false-positive cases (13%). Further analysis of the true-positive right-upper-quadrant gas signs showed that these gas collections were always triangular or linear with an inferolateral to superomedial orientation and, if triangular, a concave superolateral border. In the true-positive Rigler's signs, the bowel wall thickness ranged from 1 to 8 mm, whereas the false positives all had a bowel wall thickness of 1 mm or less. Proper interpretation of the various signs of pneumoperitoneum on supine films should lead to more accurate diagnosis of this condition.
Output:
Falciform ligament sign is characteristic to which disease?