In this experiment, would the amount of vitamin C be considered the independent

[Kelly]

variable? (I am a student using my dad's account) In my Biology class, we had an experiment wherein we had different types of fruit extracts in beakers. we dropped 20 drops of starch into each one, and then began dripping some iodine into each beaker. depending on the amount of vitamin c in each fruit extract, black particles would begin to appear at different amounts of iodine. We were given a quiz that asked us what the dependent, independent and controlled variables were, and my group put "the amount of vitamin C", as that was what caused the black particles to appear at each amount of time. When told the answers, though, we were told that the type of fruit extract was the independent variable, and that the amount of Vitamin C couldn't be it due to it being what we're trying to find. Is there an argument for the amount of Vitamin C being the independent variable and can it be backed up by scientific standards?