Possible Clues:

• Highest of everybody in exam
• A couple of students entertained by exam topping the rest
• Trade on the up in worthless goods? Most unlikely
• The biggest have an examination about everything
• Lincoln, of all the presidents
• Everyone in the exam is most lofty
• Adjective for Burj Khalifa
• Of utmost height
• Most incredible river circles a large lake
• Most difficult to believe