Christian filled two cups with equal amounts of water and placed them in a 20°C room for 30 minutes. The water in cup 1 was 5°C, and the water in cup 2 was 35°C. The diagram below shows the temperatures of the water in the cups at the beginning of the experiment.
Over the 30 minutes, Christian recorded the change in temperature of the two cups of water. Which of the following graphs best represents what he observed?