A student heat up a beaker containing ice and water. He measures the temperature of the content of the beaker as a function of time.

Which of the following graphs would correctly represent the result?

Initially the beaker contains both water and ice at $0°\text{C}$.  At that time we observe that the mixture took some time to convert total ice to water by absorption of heat energy. Hence temperature keeps constant at that time interval. Later on temperature rises with time period changes.

The correct representation between time and temperature is