Rolling marbles

This task is about planning a fair test.
Choose two cards that show how to plan a fair test to answer the question, "Will a marble roll further on a carpet or a smooth floor?" . You will need to think about what has to stay the same, and what will need to change.
a) Show your teacher the two cards you have chosen.
b) Tell your teacher why you chose those two and not two others.
 
Set of cards for each group.