The top 500 students on the open exam, or roughly 10% of all participating students, advance to the semi-final round, which will be administered in March. This second exam consists of a 120-minute long test, subdivided into two multiple-choice sections and one free response section. Part A of the exam is primarily multiple choice questions with one answer. Part B has more complex, sequenced multiple choice questions that may have several correct answers and may require calculations or extensive interpretation of graphs and multiple true/false choice questions, while Part C normally takes the form of short answers or an extended essay.