一主訴腹部急性劇痛而且身體虛弱的病人求診。仰臥胸部X光檢查和側臥腹部X光檢查（cross-table, decubitus view）呈現如二附圖。下列那一項初診斷最正確？
gas-forming liver abscess
perforated peptic ulcer
acute cholecystitis
right pneumothorax
