Death Bell (2008)

On the eve of the dreaded university entrance examinations, the lives of 24 of the smartest and brightest students at one high school are on the line. Locked inside the school with no way to escape, a television monitor broadcasts a terrified Hae Yeong, the top student at the high school, locked inside an aquarium that slowly begins to fill with water. A voice from the monitor announces if the students cannot finish the exam administered within the allotted time given, Hae Yeong will die and so will everyone held captive inside the school. Thus begins the examination that will determine whether they live or die.