Sam's science teacher assigns a project to the class in which they are to plant three mustard seeds in three different cups and monitor them for two weeks. They are instructed to care for all three seeds exactly the same, except for one difference. They will add Fertilizer A to one cup, Fertilizer B to another cup, and no fertilizer in the last cup. The cups will have the same type and amount of soil, receive the same amount of water and sunlight, and will have the same type of seed. Which part of Sam's experiment will be used as a control?

A) The control is the cup without any fertilizer added.
B) The control is the cup with Fertilizer A added.
C) The control is the cup with Fertilizer B added.
D) The control is the number of cups used in the investigation.