A student wanted to determine which material could keep her porridge warm for the longest time. She carried out the steps below:
1. She placed the same amount of porridge in containers made from different materials: A, B, C and D.
2. She measured the temperature of the porridge in each container at the beginning and at the end of 10 minutes.
The student obtained these results. Use the information in the table to answer the question.

Which material is best for insulating the student’s porridge?