15. Use the information below to answer the following question(s). Four groups of students were each given a piece of aluminum foil (20 cm 20 cm), a container holding one liter of water, and some pennies. Each group was instructed to use the aluminum foil to make a boat that would hold the greatest number of pennies while floating on the water. The dependent variable in this investigation is the:
A. amount of water.
B. number of pennies.
C. size of the aluminum foil.
D. length of the boat.