A student has 4 cups. All are equal in size and in shape. Each cup is made from a different material. The student pours an equal volume of water into each cup. The water is at room temperature (21°C). The student puts the four cups for exactly two minutes on a hot plate set at 60°C. At the end of two minutes, the student inserts a thermometer into each of the four cups and measures the water temperature in each cup. The student records the measurements in a table. By looking at the table, the student concludes that the material that makes the best heat conductor out of the four materials tested is –